Was Greece the only thing stopping a Persian invasion of Europe?

Well, this a hypothetical and geopolitical question that has no real known answer. However, I will submit a theoretical explanation that will attempt to answer your question.

First, for the historical record, a sizable part of Greece was lost to the Persian Empire during the 400's BC/BCE, it was called, "Anatolia"-(present-day Turkey). The Western Anatolian regions, such as Ionia, Lydia, Lycia and Phrygia, were under Persian colonial rule for 100 plus years.

However, Greece proper, was able, for the most part, to prevent a massive Persian colonial onslaught with numerous battle victories, the most successful and famous of battles, was The Battle of Marathon. Yet, despite Greece's various battled victories over the Persian Empire, they still suffered some defeats, including the Persian Empire's sacking and burning of Athens, as well as the famous Battle of Thermopylae-(i.e The Ancient Greek "Alamo").

But, let's say, that the entirety of Greece fell to the Persian Empire 2400 years ago, including all of its archipelagos, Crete and its entire mainland; the question is, what may have ensued?

If the Persian Empire had successfully conquered Greece proper-(similar to how the Roman and Ottoman Empires conquered Greece proper centuries later), because of its Eastern location, there is a fairly good chance that the Persians would have moved Northward into the European continent. Had the Persian Empire pursued this direction, they would have initially encountered the Illyrians-(the Ancient Albanians).

As I had mentioned in a previous posting, Illyria, was Ancient Albania, however, the original Illyrian landmass was far greater in size when compared with present-day Albania and the nearby region of Kosovo. Ancient Illyria, essentially spanned throughout much of Southeast Europe's interior, including much of present-day Albania.

It is unclear as to whether or not the Ancient Thracians, were of Illyrian ethnic descent. (My personal view is that the Ancient Thracians were a primitive Greek tribe with some Illyrian cultural influences). If, let's say, the Thracians-(the present-day region of Thrace exists in Southern Bulgaria, Northeast Greece, as well as Northwest Turkey) were of Illyrian ethnic descent, then the Persians would have encountered the most well trained of Illyrian warriors. And had the Persian Empire encountered the Thracian warriors, there is a fairly good chance that even a well trained Persian colonial military may have faced a very tough challenge. The Ancient Thracians were known to have been a fierce group of warriors and they may have prevented the Persian from moving Northward into the European continent.

But let's say, the Persians wanted to avoid all contacts with the Thracians and/or the Illyrians and instead, preferred to have colonized Mediterranean Europe. Let's say the Persian Empire had completed their conquest of Greece's Ionian archipelago-(i.e. Corfu, Ithaca, Lefkada) and wanted to conquer the Italian peninsula. (We'll exclude Sicily, since Sicily, namely, the city of Siracusa, played an important role within the lengthy Peloponnesian War and instead, focus on the Italian mainland).

If the Persian Empire attempted to conquer the Eastern Italian mainland, then they would have still encountered Greek navies who would have been dispatched from various Magna Graecia towns along the Eastern Italian town coast. If the Persians wanted to avoid the Magna Graecia Eastern Italian towns, they may have been successful in conquering parts of the Eastern Italian mainland that were populated with primitive (pre-Roman) Latin tribes. If such a scenario had worked, then perhaps the Persians would have marched into a small, but burgeoning city of Rome-(during its Early Republic phase). And from Rome, perhaps onto Ancient Tuscany-(Home of the Etruscans) and perhaps Northward into the European continent. And from Rome, perhaps westward towards the South of France, as well as Eastern Spain-(Has this scenario unfolded, then The Persian Empire would have encountered the Phoenician Empire).

Again, it is hard to envision such scenarios, because we are so accustomed to the actual historical results. Every historical scenario stated here never happened, though they are possible scenarios that may have unfolded, had Greece been defeated by the Persian Empire.

I'm not really a fan of these kind of questions. The main reason is your circular understanding of history.

Ibn-Khaldun in his Muqaddime, first one to ever analyze historical patterns in a scientific way, gives us a framework of how history moves around. In this framework history follows a circular pattern, all the events are followed by some specified events and then these are followed by other events but at the end we are going through the same reality we've already observed.

Looks kind of Hegelian to me.

Anyways, this circular pattern can be disproved easily when you look to other civilizations far beyond west or Middle East, such as those of India / americas and especially China.

It is expectable for Ibn-Khaldun to come up with this view considering the available information back then.

Anyway, you are stuck in this belief! If the Persians weren't stopped, then that does not mean they were going to dominate Europe or get stopped later on. We just can not know. We can't comment on history by looking at the past, this circular pattern does not really work. We can not make historical inferences by looking at previous inferences. History is much more dynamic, so every explanation is ridiculous on their own way.

Europe is big, Persia is far off to one side, and supply would be really long. (Living off the land would be impossible for Persia's huge army.) Thus, I don't think Persia could have gone any farther than the Black Sea and what we call the Balkans.

(What the Greek victory did do, though, was ensure that the roots of Western civilization didn't get snuffed out. That's not your question, though...)

OK. I know that I said in the comments that the short answer to the question is "yes". In fact, the short answer should more accurately be "probably".

That's because this question is an example of a particular bête noire of mine. It falls within the weird and wacky, "what-if ...?" world of counter-factual history.

(I think I've mentioned elsewhere on a number of occasions that I am really not a fan of counter-factual history. In this article, Richard J Evans sets out some of the reasons why 'What if' is a waste of time. I think he is right!)

This question is an excellent example of the problems with counter-factual history, so, just to illustrate the point, let's set out the problem:

In this case, the facts are as follows:

• The Greco-Persian Wars lasted from the first invasion in 492 BC (stopped in its tracks at the Battle of Marathon in 490 BC), to 450 BC, when the series of conflicts were effectively ended with the Battle of Salamis-in-Cyprus.
• The Greeks won.
• At this point in time, the Greeks were the dominant civilisation in the eastern Mediterranean (although Greece was by no means a unified nation, as would be shown with the outbreak of the Peloponnesian War in 431 BC).

So what else do we know?

• Carthage was the commercial centre of the western Mediterranean with colonies extending into the Iberian peninsula.
• Rome was beginning to establish itself as a major power in Italy, with its early Italian campaigns running from 458–396 BC.
• In Europe to the north were "the Celts". Our understanding of exactly who "the Celts" were, the structure of their society, and how effective they would be as a fighting force in the early fifth century BC is, at best, imperfect. We know that the Celtic army that invaded Italy in 390 BC, and defeated a large Roman army, was formidable. It is much harder to say with any confidence how effective a Celtic army would have been as a fighting force against a large organised army a century earlier.

So, now to the "counterfactual" bit.

We imagine that Greece lost. How would Rome, Carthage and "the Celts" have fared?

• Carthage was predominantly a maritime power at that point. Perhaps we could reasonably expect that they would have given the Persians a run for their money at sea. However, so much would have depended on tactics that I don't think we can even be confident of that.
• What about the land forces? From what we know of the "factual" histories of the period, there isn't much to suggest that the land forces of either Rome or Carthage would have been a match for those of Persia. But once again, tactics count for so much.

The Persians outnumbered the Greeks by at least two-to-one at Marathon, and the Greeks were fighting without the Spartans. A "counterfactual" history might have postulated a Persian victory given those facts, and the "counterfactual" history would have been wrong.

(Similarly, given the relative known facts of the armies at the battles of Crécy and Agincourt, a "counterfactual" history might well have anticipated a French victory. Ah well!)

• So what about the Celts? Well, for a start, how interested would the Persians have been in conquering the Celts? As far as we know, the Celts didn't have much that the Persians would have recognised as the trappings of "civilisation" at that point. Perhaps the Persians would simply have regarded the Celts as "barbarians" and "not worth the trouble". Alternatively, perhaps they would have pushed on to complete their "conquest of the world". If so, how would the Celts have fared against a massed Persian army? We simply don't, and can't, know.

With that many unknowns, we are heading into the realm of guesswork, bordering on fantasy!

So, let's get back to the question. If the Greeks had fallen and were taken under Persian rule would there have been any force in Europe capable of preventing a complete annexation of Europe?

Probably not, but the Greeks didn't fall, so we will never know.

Was Greece the one and only stand?

The Greco-Persian Wars included two invasions of Greece and a number of Greek counter-attacks against Persia, so "one-and-only" certainly wouldn't be how I would phrase it. Beyond that, as I said, we are in the realm of counter-factual history, and so we will never know.

Did I mention that I am really not a fan of counterfactual history?