Do historians agree that most wars are caused by religion?

I have never read such a theory, by any historian. This is likely because few real historians have ever made the claim.

I think we can easily see why that is: To be "most" it must be over 50%.

But not all religions are warlike. And not all warlike religions can be used to justify/launch wars.

Buddhism, Hinduism, Taoism are non-warlike religions. And they can most certainly not be used to justify wars (the god of those religions can't be owned by a group of followers. And those gods never made any promises, and never demanded the followers to find new followers)

Shintoism is warlike religion but it can't be used to start wars. because it isn't a god-owning religion.

Mesoamerican religions are not overly well understood, but given they didn't launch a holy war against the foreign invaders it seems pretty clear that holy war wasn't their thing. Native americans also don't have a war like religion.

Right there, that's more than 1/2 the world, and probably more than 1/2 the wars ever fought.

Then there are a few religions that are both warlike and war justifying. This is made possible by a custom made god that institutionalizes racism, makes land grant, and gives a religious mandate to spread the truth of 'love', 'peace', 'hope', 'chosen' and 'faith' to anyone lacking in 'love', 'peace', 'hope', 'chosen' and 'faith'. And if the infidels, heathens, nonbelievers, etc. refuse to accept the truth, the followers are encouraged to convert them, by force if necessary.

But even then, not too many of the wars by the adherents were actually fought in the name of those religions. And most of the biggest ones were all religion free. Napoleonic War, Franco-Prussian War, WWI, WWII, the 100 years war, the 30 years war, the crimean war, etc. That doesn't mean each side didn't bring their holy men with them to war, to ask their god to smite down those other guys in the opposing army.

So I would say a tiny percentage of wars are caused by religion, the rest are caused by kings playing the game of thrones.

Historians, by and large, agree that most wars fought for resources and thus are caused by the greed for worldly or physical gain, be it land, women or money. See: "Encyclopedia of Wars," by Charles Phillips and Alan Axelrod.

However, in order to motivate the masses, they used religion as a motivational tool. This still works today, given how many use Christianity as a motivation to be a conservative. This is ironic, given that that religion was essentially a rebel movement, against the Roman Empire and decidedly not a conservative cause. Therefore, while religion itself might not cause wars, it does acerbate them because religion is used as a justification. Joan of Arc, the Civil War, Colonial wars would not have had this effect had it not been for the religious motivation. And it's doubtful that Joan of Arc would have gone to Germany or Africa to fight perfidious Albion.

As a side effect of triumphantly decrying that religion is NOT a cause of wars, some play the fake victim card: "Oh, us poor Christians, who are oppressed by the evil atheist hordes."

Other answers are justifying a straight "no", but what else is going on in the "critique of theism" mentioned by Semaphore?

The atheist philosopher Tim Crane addresses, in his book "The Meaning of Belief" (2017, Harvard University Press) claims of this kind that are made by certain atheist critics of religion (so, his subject is not any supposed consensus among historians). Spoiler alert: his view of attempts by famous atheists like Dawkins or Hitchens to analyse religion is not broadly approving. What does he say about claims that religion is wholly or mainly responsible for war and other violence? p120-122:

The violence and destruction imposed in the name of Christianity has a long history: the medieval Crusades ... [4 further examples]; and we could go on, of course. Put like this, you can see why people say that the history of Europe in the second millennium AD was a history of religious violence.

Against this has to be placed the equally terrible history of large-scale nonreligious violence and cruelty. Examples easily spring to mind: the killing of the Central American natives by the conquistadors, the slave trade, ... [4 further examples]. And then of course there are the other monstrous crimes of the twentieth century: the Nazi Holocaust and the mass killings by the communist regimes in China and the Soviet Union. As with religious violence, it seems all too easy to find examples.

Some writers more sympathetic to religion attempt to argue that those examples show that religion is not really the source of the world's problems, and that even so-called religious conflicts are not really religious underneath. ... Karen Armstrong traces the origin of human violence to the beginnings of agrarian societies and the accumulation of wealth...

The account I sketched of identification in Chapter 3 of this book indicates one other place where an explanation of of religious violence that is not specifically religous might begin. The tendency of human beings to form groups explicitly defined in opposition to others, which then seek the destruction and subordination of the other groups, is one of the characteristic features of many recognizably human societies. But facts like these do not mean that religion has no special, distinctively religious role in explaining episodes of violence. ... The question is rather, what is this role.

He goes on to point out that even wars that some attribute to religion are not necessarily caused by any theological content of the religion. p132:

It would be entirely incorrect, even frivolous, to suggest that the filoque clause is one of the factors that influenced the war between the Serbs and the Croats in the 1990s. And yet, if we are to look at the theological origin of the separation of the Roman and the Orthodox Churches, this would have to be mentioned (among many other details) ... yet it is plain that this doctrine has nothing more to do with the war than the fact that the Serbs use the Cyrillic alphabet and the Croats use the Latin alphabet.

So, what is there to religion other than theology? Well, that's the major part of the book, and his view is that religion consists of group identification, together with the "religious impulse" toward something that transcends normal life, connected by a shared notion of what specific things are sacred. Hence, there are other ways that religion could be a factor than just theology. p134 returns to the causes of religious violence:

I mentioned three further conjectures about the sources of religious violence and conflict: (2) nontheological but distinctively religious aspects of religions; (3) the element of identification; (4) other nonreligous aspects of human psychology, society and culture.

p143:

Religion is one factor, without doubt. But is it the most fundamental or important factor? How can we go about answering this question? Is there even any need to answer it? ... The extreme violence in these cases is often explicable in terms of the tendency of identification (religious or not) to exclude and discriminate against others; the violent content of some religious texts; or the struggle for power, supremacy, or autonomy among competing religious groups--in addition to human motivations and desires (for example, revenge) that are intelligible independently of anything to do with religion.

There's plenty more detail, but his gist is that what constitutes religion "causing" violence (or a war in particular) is by no means a simple or settled issue. That being the case you can't really have a simple, settled view of whether religion is uniquely culpable among other factors.

So the claim that "most wars are caused by religion" may not even be intelligible. Do most wars have religion among their causes? Are most wars caused solely by religion? What aspects of religion can be included or excluded in the assessment of whether religion caused something? You're going to do a very different analysis according to how you interpret the basic structure of the question, never mind your actual historical opinion about the causes of every war.

Q Do historians agree that most wars are caused by religion?

Most historians agree that most wars cannot be described with a monocausal reason.

There is a big bunch of problems associated with asking the question in this way. Definitions, conceptualisations, perspective, timeframe and grammar are all undetermined or off. Is this about whether the claim as such is true or about an assumed majority opinion of historians; now or previously?

Just a thought: Who started the Global War on Terrorism? The Americans? Al-Qaeda? For what reasons (aka "cause")? Is religion the main causative motivator for the American led forces? Is it for "the other side"? Perhaps a minority might answer yes to religion as a motivator for American forces, but surely most will accept the narrative that bin-Laden and his followers were primarily religion motivated? Or do they emphasise his apology that he became offended when American troops were stationed on Saudi-Arabian soil, making this again about land and territory, 'holy' or not? But perhaps it is different yet?

Bush’s war openly remains a cosmic battle between nothing less than the transcendent forces of good and evil. Such a battle is necessarily unlimited and open-ended, and so justifies radical actions–the abandonment, for example, of established notions of civic justice at home and of traditional alliances abroad.
_{James Carrol: "The Bush Crusade. Sacred violence, again unleashed in 2001, could prove as destructive as in 1096.", The Nation, September 2, 2004}

Historians do not always agree on a subject matter of the past. Historians diverge very widely if it is about how to apply those insights from the past to the present day. If you want to know historians view on what the reasons for war are, then a number of people will say this or that.
Samuel Huntington, for example, views that civilisations or cultures are clashing –– and were for some time now. The main differentiator of a culture by this definition is its religion. Therefore, those sympathising with the Huntington school assume that most wars are caused ultimately by religion.

But leaving aside the semantics over grammar and resultant meaning of "are caused", it seems that there still is an anachronistic and eurocentric vision dominating the way this question was to be answered here.

This question is about religion in general, not about Christianity, Islam or any form of monotheistic religion? Then religion is a prime motivator for ingroup-outgroup behaviour. It represents the core of order for any civilisation against the chaos. And therefore for war in general. We do not have to reduce "religion" to "any form of some belief" to approach the problem. Otherwise, it gets trivial: "we believe that this strip of land belongs to us, we believe to need that etc"; we believe capitalism to be so much better for mankind".

Going into a structuralist or functionalist mindset we might say that sure, religion needs a base from which to perform. So a religious motive is in reality about power, and that is about power over the inhabitants, and that is over the lands on which those inhabitants live. Muslim expansion is then nothing about any form of to invent or develop a form of Islam, just land grabbing of Arab conquistadors who happened to eventually provide an ideological superstructure to justify the new rule and system of power distribution and organise a changed set of alliances between rulers and ruled.

If we ask the propagandists for war from the past, then we have to first reflect on the nature of state and religion in general. It was indistinguishable. Romans fought a bellum sacrum, Christians had Crusades against Muslims, Albigensers, Prussians; earlier Charlemagne brought Christianity by sword to the Saxons, native Americans; Muslims conquer India, Hindus fight the Muslims, English Christians wanted to mission the world with tea, opium and Christianity for the betterment of humanity. Muslims have their jihad to this day. The Incas were weakened when Christian Spanish arrived to conquer those pagans because of a civil war to determine who really was the legitimate descendant of Inti, the sun.
Mayans had their star wars, Aztecs flower wars. The latter from a modern perspective for no particular reason, other than to capture people to be used in human sacrifice. That looks as if there is nothing else but a religious motivation in those kinds of wars. Romans inquired the auspices before going to war than performed a religious ritual on the mars field, performed evocatio deorum before the enemy's city gate, then captured the city god and added it to their own pantheon. The Hittites performed exactly likewise.

Is there any war or warlike conflict in the Bible or the early Jewish history that is not entirely about religion? The taking of the promised land, the wars against Jericho, Ai, Israel & Judah, the Maccabean Revolt, the at least three full Jewish Wars against Rome?

It can very well be argued that it is universally true, that before the 'modern state' and the ideas of separation of church and state, religion was one prime cause for all the wars.

Or it is true that rulers and generals always lie. That what really was or is the cause is always something else. All marxist historians would agree to that. And Clintonistas as well. It's the economy, stupid.

The prime motivation as stated by instigators might then be "religion", although it really is about something else: the means to rule; in form of land, labour means of production. Those who follow Claude Levi-Strauss will of cause know it even better than that: all human conflict can be broken down to disagreements over the exchange of women. Let's not forget reductionist explanations like those from an offshoot of psychoanalysis. War is an illness in society and all of society's illnesses can be cured by achieving a proper o*g**m. –– If that sounds ridiculous, then looking for mono-causality of war, for any war, in the thousands of years for its history is likely as well.

Religion is one of the most powerful forces in human history, and its power makes itself known in ways both dramatic and intimate in our world today; unfortunately, the impact of religion is often divisive and violent. If we want to truly understand religion’s ability to influence human events, we need to grasp its psychological bases, and to take a scientific approach to religious psychology means using our best theories of how the mind works.
_{John Teehan: "In the Name of God. The Evolutionary Origins of Religious Ethics and Violence", Wiley-Blackwell, 2010.}

_{Martha T Nussbaum: "Democracy, Religious Violence, and India’s Future",}

This is one of history's ironies, that although religion has been used to justify violence, violence can also empower religion. Perhaps understandably. therefore. in the wake of secularism, and after years of wait· ing in history's wings, religion has made its reappearance as an ideology of social order in a dramatic fashion: violently. In time the violence will end, but the point will remain. Religion gives spirit to public life and provides a beacon for moral order. At the same time, it needs the temper of rationality and fair play that Enlightenment values give to civil society. Thus religious violence cannot end until some accommodation can be forged between the two-some assertion of moderation in religion's passion and some acknowledgement of religion in elevating the spiritual and moral values of public life.
_{Mark Juergensmeyer: "Terror in the Mind of God: The Global Rise of Religious Violence", University of California Press: Berkeley, London, 2000.}

To understand the role of religion in the emergence of American empire, we need to look beyond any simple opposition or interaction between “church” and “state” and see instead how the construction and corrosion of power and authority have operated across sectors of society, especially around apparently “secular” categories in which the displacements of religious logic have most effectively operated under assertions of innocence, purity, or transcendence. ose categories through which the material origins of desire have most consistently been compressed and displaced in America are age, race, and gender, as expressed in the culture in various identities associated with collectives like the nation or, now, an empire.
_{Jon Pahl: "Empire of Sacrifice. The Religious Origins of American Violence", New York University Press: New York, London, 2010.}

Violence served to uphold the Egyptian concept of correct order, known as Ma'at. Some violence, such as sacrificial servant burial, did so by ensuring that correct social order continued in the next life. Most violence in the service of the order was aimed at the destruction of chaos, or Isfet.
_{Kerry Miles Muhlenstein: "Violence in the Service of Order: The Religious Framework for Sanctioned Killing in Ancient Egypt", Dissertation, University of California: Los Angeles, 2003.}

Much has been written about the relationship between religion and violence, and much of what has been written is aimed at determining whether, how, and why religion causes violence. This book has a different goal. Followers of many different religions who commit violent acts seek to justify these by appealing to religion. I aim to understand how such justifications proceed; and how they do, or do not, differ from ordinary secular justifications for violence. I will show that religious justifications for violence generally exemplify the same logical forms as ordinary secular justifications for violence. I will also show that many religiously based justifications for violence are as acceptable as rigorous secular justifications for violence, provided that crucial premises, which religion supplies, are accepted. Religious believers are able to incorporate premises, grounded in the metaphysics of religious worldviews, in arguments for the conclusion that this or that violent act is justified. I examine three widely employed types of premises that appear in such arguments. These are: appeals to a state of “cosmic war,” appeals to the afterlife, and appeals to sacred values.
_{Steve Clarke: "The Justification of Religious Violence", Blackwell: Chichester, 2014.}

The Enduring Relationship of Religion and Violence / Violence and Nonviolence at the Heart of Hindu Ethics / Buddhist Traditions and Violence / Sikh Traditions and Violence / Religion and Violence in the Jewish Traditions / Religion and Violence in Christian Traditions / Muslim Engagement with Injustice and Violence / African Traditional Religion and Violence / Religion and Violence in Pacific Island Societies / Violence in Chinese Religious Traditions
_{Mark Juergensmeyer & Margo Kitts & Michael K. Jerryson: "Violence and the World’s Religious Traditions. An Introduction", Oxford University Press, 2017.}

In addition to the good answers given already, I'd like to point out that wars are typically not mono-causal. Very often, several reasons as well as causes (i.e. sparks that light the fire) come together for a war to start.

In addition, the reasons given in public are often not the actual reasons. There are a number of explicitly religious wars (the Islamic conquests of Europe, the European answer aka The Crusades). In many other wars, religion played a role in the "us vs. them" sense - religion is one of the factors that bind people together and separates them from other people, just like language, skin colour, etc. It is easier to start a war against "others" than against "like us".

And finally, there are many parties involved in wars. The head of state might declare the war, but there are so many different people with interests involved and for some of them a financial profit might be important, for some of them territorial gains, and for some of the religion. These goals also change during the course of a war or in parts of the war. For example, JMS gave "revenge" as the reason for WW2, but the attack on Russia had other reasons, and the war in North Africa was purely for resources. Meanwhile, WW2 also had the Asian part with Japan as the aggressor, which again had different reasons to start their part.

Identifying one reason for a specific war is most likely an oversimplification. So the question as phrased doesn't even make sense because it asks to identify a mono-causal relationship which in reality does not exist.

Religion certainly played a role in most pre-modern-times wars, though it was more often used as a cover for more simple desires (taking land, resources, disputes over hierarchy or succession, etc.) than the other way around.

I'm not a professional historian, just interested in history. From what I've found in books and other resources, historians would not, in general, agree that anything is the #1 source of wars, simply because wars are not so easy. That begins with the difference between reason and cause - between what the background of the conflict is and what often small spark caused the conflict to finally erupt. WW1 is a good example for that, it was caused by the assassination of Archduke Franz Ferdinand, but if that hadn't happened, something else would have most likely caused the war that everyone was pretty much waiting for.

That makes it difficult to ascertain if religion contributes to that background. For the king or whoever, it is certainly easier to start a war if he can also add religious reasons to the motivation. The 30 years war is an example where religion played a major role, but many other often regional causes added to the mix until the whole thing exploded.

Do historians agree that most wars are caused by religion?

No, historians have not formed such a consensus. There are numerous scholarly works reaching back 5 millennia demonstrating that this belief is apocryphal. This work demonstrates religion historically has played a small role in wars either as a major or minor cause.

Is Religion the Cause of Most Wars?
History simply does not support the hypothesis that religion is the major cause of conflict. The wars of the ancient world were rarely if ever, based on religion.

...an objective look at history reveals that those killed in the name of religion have, in fact, been a tiny fraction in the bloody history of human conflict. In their recently published book, “Encyclopedia of Wars,” authors Charles Phillips and Alan Axelrod document the history of recorded warfare, and from their list of 1763 wars only 123 have been classified to involve a religious cause, accounting for less than 7 percent of all wars and less than 2 percent of all people killed in warfare.

A Different source: The Encyclopedia of War edited by Gordon Martel says if one excludes 40 little understood internal wars fought by the Islamic Caliphate religious wars drop to only 3% of all wars in its pages.

Institute for Economics and Peace issued a report in 2014 which further supports these numbers.

So Historians, reviewing 5 millennia worth of war, have reached the opposite conclusion. Religion is a reason for war, but not the reason for most wars.

Wars are often blamed on a single reason but typically caused by a combination of reasons. Yes Religion is among the reasons historically countries go to war, it is even a primary cause of some conflicts like the Crusades, Thirty Years' War, and the Lebanese War 1975-1990 Religion is not the primary reason historically speaking for most wars.

Common (major and minor) Reasons for War:

1. Economic gain: (oil, natural gas, nickel, etc ).

• Anglo-Indian Wars (1766-1849)
  A series of wars fought by British East India Company leading to the colonization of India.
• The Winter War (1939-1940)
  The Soviet Union invaded Finland in order to control the nickel mines.
• The American Revolution
  For America a revolutionary war, for the French who allied with the United States against Britain it was fought over trade routes and commerce. The French involvement began first with a trade agreement with the Colonies and only after that was signed a declaration for French military assistance against Britain.
• WWII, in the Pacific The Japanese attacked Pearl Harbor in order to seize commodities in Asia.
• Iraq's invasion of Kuwait.
  Iraq invaded Kuwait to seize the oil and alleviate their war debt with the Kingdom.
• South China Sea
  The ongoing dispute with China over the South China Sea, It's about 11 billion barrels of untapped oil and 190 trillion cubic feet of natural gas estimated to exist in the disputed territory.

2. Territorial Gain

• Mexican-American War (1846-1848). It was a land grab. The slogan manifest destiny spoke to the United States desire to become a two Ocean country. (Atlantic and Pacific). The War facilitated the United States purchase of what is now the American South West as well as California.
• Arab-Israeli War or "Six Day War" (1967-1988)
  After years of small-scale conflict when Egypt blockaded the straight of Tiran, Israel attacked gaining the Sinai Peninsula, the West Bank, and Golan Heights effectively tripling the size of the Israeli state.
• Russia's invasion of the Crimea (2014)

3. Nationalism

• World War I

4. Revenge

• World War II (invasion of France by Germany) One of Hitler's stated reasons for invading France was to reverse the Treaty of Paris which ended WWII which he felt treated Germany unfairly and was a factor in Germany's impoverishment in the interwar period. He met with French representatives in the same train car which hosted the WWI summit which ended the Great War and even had the memorial in Paris to the historic treaty blown up.

5. Civil Wars and or Revolutions
   Fought over disputes which arise internally to countries or over a change of leadership.

• American Civil War (1861-1865)
• Russian Civil War (1917-1923)
• Spanish Civil War (1936-1939)
• Korean War (1950-1953)
• French Revolution (1789-1799)
• Haitian Revolution (1791-1804)

Addressing the Comments

Steven Burnap
"Lebensraum" was an explicit aim of Germany in WWII. The Japanese actions that lead to WWII in China, as well as their invasion of the Philippines, was also very much about gaining territory. Though this really just goes to show that history usually doesn't fit into neat categories. "Religious war" being a neat category.

@Steven Burnap, Hitler's book Mein Kampf, was written in two volumes, The first volume, entitled Die Abrechnung (“The Settlement [of Accounts],” or “Revenge”), calls for revenge against France for its destruction of Germany's first and second Reichs.

Specifically, Hitler discusses the 30 Years War in which Germany's first Reich (Holy Roman Empire) was eviscerated by the French in 1648, with the Peace of Westphalia. Secondly and famously the treatment of Germany in the surrender documents ending WWI which both impoverished Germany in the interwar period and ended Germany's second Reich, Imperial Germany ()1871–1918 ending Kaiser Wilhelm and the end of WWI.

In Hitler's first volume he dedicates the title to the major theme of his foreign policy. Revenge against France. To your point Hitler also discusses "Lebensraum" in his first volume, the need for "Living Space" for Germany and says Germany will gain this in the east at the expense of the Slavs: Czechoslovakia, Poland, Belarus, Ukraine, and Russia.

A major stated goal of Hitler's Third Reich was to address the downfall of the first and second German Reichs at the hands of the French. In June of 1940, Hitler drove this point home with what National Geographic calls his Revenge Treaty in which France surrenders to Germany June of 1940. Hitler held the surrender ceremony in the same boxcar in which France had hosted Germany's surrender in WWI. Designed the entire venue to embarrass the French referencing Germany's previous treatment by the then victorious French in WWI. Just after this ceremony Hitler personally ordered Frances Rethondes Clearing memorial to WWI's German surrender blown up with dynamite.

As for Japan's war in China, I don't dispute what you say. What I said was Japan attacked the United States, Dec 7, 1941, over oil. The attack was to clear obstacles to Japan's real target of that offensive, the Dutch East Indies -- now Indonesia.

On July 26, 1941, the American President Franklin D. Roosevelt signed an executive order which froze Japan's assets in the United States and cut Japan off from 93% of their Oil all of which was imported. Japan had about a year and a half of oil in their strategic reserve and after that, they would not be able to continue their war in China. Japan attacked Pearl Harbor on Dec 7, 1941; and invaded Dutch East Indies Dec 8th to secure what was then the 4th largest oil exporter in the world behind the U.S., Iran, and Romania and guarantee Japan would be energy independent. Japan also gained access to rubber production facilities and iron mines both of which were important, but oil was the most important material they seized in the days after Pearl Harbor.

Japan's Dutch East India Campaign
Access to oil was one of the linchpins of the Japanese war effort, as Japan has no native source of oil;15 it could not even produce enough to meet even 10% of its needs,13 even with the extraction of oil shale in Manchuria using the Fushun process.16 Japan quickly lost 93 percent of its oil supply after President Franklin D. Roosevelt issued an executive order on 26 July 1941 which froze all of Japan's U.S. assets and embargoed all oil exports to Japan.17 In addition, the Dutch government in exile, at the urging of the Allies and with the support of Queen Wilhelmina, broke its economic treaty with Japan and joined the embargo in August.15 Japan's military and economic reserves included only a year and a half's worth of oil.13 As a U.S. declaration of war against Japan was feared if the latter took the East Indies, the Japanese planned to eliminate the U.S. Pacific Fleet, allowing them to overtake the islands; this led to the attack on Pearl Harbor.