What were Germany's long-term aims in World War I?

Territorial annexation goals do not tell the whole story. It's the economy, Stu…
Of these annexationist fantasies there were quite a lot going around during the war, and quite significantly: before the war. Obviously, they weren't all identical, but they tended to coalesce around a certain kernel of aims. It was for Germany to become the undisputed hegemon of continental Europe, and as such the leading world power.

More important are the relational shifts the German side envisioned. Economic and other power parameters should be altered in favour of Germany, permanently. As such any British influence should be kept 'from the continent', France and Russia diminished in their roles and abilities. The rest would then follow 'naturally'. Wherever an inhabitant was speaking the German tongue, that settlement was ripe for incorporation into the Reich, wherever no-one speaking German could be found but the land was still 'in Europe', that should be added to an economic free trade union under German leadership. Some would term that zones or spheres of influence, or even 'puppet states'. But these words look like slightly outdated propaganda vocabulary.

In short: a continental power bloc, led by Germany, but not in all its parts called 'Germany'. That is: some kind of 'union', in 'Europe', focussed on economic integration, and common defense.

They tried to think of a nice name for that. And they came up with: — 'Mitteleuropa'.

Yep. I know. This sounds like to create in the reader's mind an allusion to the "European Union". As it is now. Alas, that contraption of words was just not that popular back then. But it was thought of! An it was thought of a union of common interest, standing together combined, "against all English speaking countries" (as they were seen as much more aggressive; the whole following piece is not typical for German conservative Weltanschauungen, but illustrates nicely how essentially Napoleonic maps would be sold under Germanic hegemony):

— Leroy-Beaulieu: "Über die Vereinigten Staaten von Europa", Die Umschau, Vol 4, No 37, 8 Sep, 1900, p724.

In other parts of the world they thought of creating an enlarged and continuous empire, by acquiring large parts of Africa, surrounding their previous possessions and adding to that a few strategic bases around the world, like they had in China or the South Sea: Tangier, Cape Verde, Goa, Ceylon, Azores, Saigon.

This sounds very much like, and will look like in the maps I'll present to you very much like the German nazi plans for Lebensraum and colonial empire for world domination we saw in World War Two. And they are almost identical. Germans are said to be good at 'recycling', in this case ideas. There are then much less grandiose plans of the madman Hitler, but a much less creative continuity of German foreign policy and strategic goals. To be clear: imperial Germany was a deeply racist and conservative state, with ample antisemitism going around. But still the fate of Eastern Europe's population was not one of extermination of Jews or Helot-like slavery for the slavs.
While such tendencies existed already in the practical administration of Ober-Ost and in the minds of some of the German officials and military there, the added extremism of genuine nazism came a short time later. What we have in 1914 is an atomising analysis of ethnicities in the East, a divide and conquer plan for Russias minorities, like Whiterussians, Ukrainians, etc. And a line of planned expansion that comes awfully close to the nazi-plan of an AA-line.

The imperial German goals were shared to a degree by the administration, government, and military, the Kaiser, the politicians and for large part the general public.

As a not only 'added benefit', a rally around the flag should strengthen the patriotic feelings and conservative power base: war would bring about Burgfrieden to silence proletariate, workers, social democrats and glorify a charismatic since victorious leadership; expansion into the East was primarily in settling and Germanising the land, thus diverting from the numbers of red-leaning workers automatically. These thoughts are analysed under the motto: 'primacy of domestic policy'.

The date when these deliberations left academic discourse and entered public and political debate would have to be set to the era of Neuer Kurs (new course) under Wilhelm II and his chancellor Caprivi. The end of Bismarck's "Germany is saturated" and onwards to Wilhelm's "our place in the sun":

The exploratory talks of German diplomacy with the aim of "achieving agreement on the approach of the central European powers simultaneously affected" had, however, come to nothing in Paris, Vienna, Madrid, Rome and London in view of the heterogeneous points of interest, but above all also because of the fundamental reservations in France. The trade agreement policy pursued by Caprivi prompted the head of the trade policy department of the Foreign Office, von Berchem, in its internal preparatory stage, to consider the anti-Russian concept of a trade policy alliance on the basis of differential tariffs once again as urgent.

However, Caprivi, encouraged by memoranda with contrary opinions, considered such plans, which were also described in the Foreign Office as "dreams of the future", to be somewhat unrealistic. After all, Caprivi took the "Central Europe" plans seriously enough to use them to promote the trade agreement policy of the "New Course" in the Reichstag:

"If the European states want to maintain their position in the world, they will not be able to avoid being closely aligned. It is not impossible that the time will come when they will realize that they have smarter things to do than suck each other's blood, because in the economic struggle for existence they will be forced to use all their strength."

With this emphasis Caprivi won widespread support across the factions. Even in the ranks of Socialist MEPs, the keyword "United States of Europe" made an impression. […]

As little effort was made to allay such fears, so little was the concept of an alliance of equal rights and obligations for the nations have ever been in the vicinity of the German "Central Europe" discussion. A constantly recurring topos remained, especially in the light of the naval propaganda that began at the turn of the century, the talk of "one last great division of the earth". The advocates of a Central European economic bloc were referring to the German Empire's delay in "dividing the world" and accordingly propagated a return to the continental power base. Gustav Schmoller, in a much-noticed "secular view" of European trade policy in the 19th century, assumed a quasi natural trend towards the formation of hermetic large economic areas. In addition to American high-protection customs policy, it was the British plans to establish an Imperial Customs Union that provided the advocates of a Central European economic bloc with their most important arguments.

_{— Peter Theiner: "'Mitteleuropa': Pläne im Wilhelminischen Deutschland", Geschichte und Gesellschaft. Sonderheft, Vol. 10, Wirtschaftliche und politische Integration in Europa im 19. und 20. Jahrhundert (1984), pp 128–148.}

These considerations developed in the process and had almost always in common the aporia that Kurt Riezler, a politically intimate advisor for Bethmann-Hollweg and author of the Septemberprogramm, had noted as early as 1915 and whose violent implementation was reserved for National Socialist expansion:

Evening: long discussion about Poland and the possibility of a looser annexation of other states to the Reich - Central European system of differential tariffs. Great Germany with Belgium, Holland, Poland as close, Austria as wide protective states.(p198)

"I always drill at a German supremacy over Central Europe and all small states under the guise of a Central European confederation without loss of German power."(p253)

Yesterday we sat for a long time with the Chancellor to discuss my new Europe, i.e. the European enhancement of our will to power. The central European empire of the German nation. The nested system customary in joint-stock companies, the German Reich a joint-stock company with a Prussian share majority, any addition of new shareholders would destroy this majority, on which, as the Prussian hegemony, the Reich stands. Hence around the German Reich a confederation of states, in which the Reich has the same majority as Prussia has in the Reich - hence Prussia has the actual leadership in this confederation. To solve the Belgian question in such a way that it does not stand in the way of this future development, but on the contrary helps to bring it about itself. Then treat Austria in such a way that it grows into it by itself. […] Then strengthen the European idea in Scandinavia and Holland […] This Mitteleuropa is the economic and political task of world history.(p268)

_{— Karl Dietrich Erdmann (Ed): "Kurt Riezler, Tagebücher, Aufsätze, Dokumente", Vandenhoek & Ruprecht: Göttingen, 1972, (p253).}

As such any analysis of this subject cannot refrain from looking at the seminal work of the German historian Fritz Fischer. He summarised these undeniable continuities in his first major work called "Griff nach der Weltmacht, die Kriegszielpolitik des Kaiserlichen Deutschland, 1914–18. (1961)." ('Germany's grab for world power', translated into English as only the second part of the title: Germany's Aims in the First World War. In this book the Septemberprogramm first came into the public eye.

The book caused a scandal among right-wing leaning German historians at the time, as one of the implications from that (which Fischer did not make explicitly at the time), would have been that the 'war guilt paragraph' of the Treaty of Versailles that blamed Germany alone for the 'outbreak' of the war would have been an accurate description. (That's not the case though, as Austria, France, Britain and Russia at the very least very much also contributed to that. While much too apologetic, cf eg Christopher Clark's 'Sleepwalkers'). After some fierce debates, and a few more studies reaching the same conclusions, Fischer's own main findings are no longer under dispute or even doubtful. His own later works just add to that mountain of evidence. (Also look at his other works, like "War of illusions : German policies from 1911 to 1914" that shows how this was very well part of the programme, before the world war started… In terms of historical philosophy, a Hegelian inevitability of the next war informed much decision making.)

It should be emphasised that Riezler's Septemberprogramm, was itself not public knowledge at the time in 1914. It was a kind of most common or least common denominator compromise that chancellor Bethmann-Hollweg sought to appease all sides in the debate: The Alldeutschen, the Navy League, the military on land as well as the navy itself, the industrial capitalists, the agrarian capitalists and so on. It is most significant for how it formed a picture of the base of discussions that existed before the war and how the different ideas waxed and waned around those visions of grandeur but had to adopt to 'realities on the ground' as well as changing desires of annexationists and economic planners.

Especially the Alldeutschen had this to say, in 1894 in one of its first publications, the 'Alldeutschen Blätter', to which the internal 'compromise' offer of 1914 war aims in Septemberprogramm has to be read:

To the East and Southeast we must gain elbow room in order to secure for the Germanic race the living conditions it needs to develop its full strength, even if such inferior peoples as Czechs, Slovenes and Slovaks (…) were to lose their existence, which was useless for civilization (…) German colonization, German industriousness and German education (…) were to serve as a binding agent as far as Asia Minor, through which large and future-rich economic areas (…) would join us.

Buy it at the kiosk!

These early Alldeutschen demands were in comparison quite moderate. In 1908 they make the outspoken antisemite Claß their new chairman. And he radicalises ever more for the next 30 years.

In 1909 already Claß propagated as an alleged 'conclusion from history' that Germany had to direct its expansion policy primarily towards the East. He accused the ruling circles of the Empire of having pursued a "weak" foreign policy since 1890 and demonized the Social Democrats as well as the members of the Centre Party and the Free Democrats as "pests". Claß called for another war aim in itself: war! And for a dictator – and in the event that he would lead Germany into a great war, he declared:

So much the better for our people! Then the war will make them well, and misery and tears will reawaken their moral strength, and the cannon thunder will disperse the clouds; they will prove their heroic strength and find their heroism again, and return home from the bloodbath of battle, strengthened and richer, despite all the losses of life and property. Then the way into the future would be clearer for us all the more!
_{— Einhart (Claß pseudonym): "Deutsche Geschichte", Dieterich: Leipzig, 1909.}

As the Septemberprogramm summarises itself:

Securing the German Reich to the East and West as far as possible. To this end, France must be weakened in such a way that it cannot be reestablished as a great power, Russia must be pushed off the German border as far as possible and its rule over the non-Russian vassal nations must be broken.

This leads to researchers concluding:

Fischer irrefutably demonstrates, as was already evident with particular clarity from the work of G. Gratz and R. Schüller, which he did not cite, the extent to which the interests of German industry determined the German war aims.

Especially in view of the emphasis Fischer places in the main part of his work on the intentions of economic domination and exploitation of the territories in the German sphere of power, […] […] he says that the Upper Silesian industry had brought Polish mines and Polish ore "up to Radom" under its control through strong capital participation, that German heavy industry was interfering in the Ukrainian and Caucasian raw material areas of Krivoj Rog and Ciaturi (Thyssen's interest in the ores of the Danube region and the manganese of the Caucasus), and that the German banks were expanding their relations with the Russian banking world with regard to the armaments business; he also mentions the strong German economic interests in Romania…
_{— Fritz T. Epstein: "Die deutsche Ostpolitik im Ersten Weltkrieg", Jahrbücher für Geschichte Osteuropas, Neue Folge, Bd. 10, H. 3 (Oktober 1962), pp381–394.}

As perhaps the main 'discussions of war aims' during the war and how these affected events and outcome of the war and peace treaties are discussed well in — Nils Löffelbein: ("War Aims and War Aims Discussions (Germany)", 1914-1918-online. International Encyclopedia of the First World War, 2017.) I just link to them there.
Here, we'll look at nice maps now.

First Mittelafrika (as also discussed here)

Now Mitteleuropa:

Notice the arrows to indicate that Persia and India were next on the list of directions to expand power into. And how well the Peace Treaty of Brest-Litowsk was used as an achievement and a spring board.
_{(Src: Fischer, War Aims)}

If that sounds like Fischer making things up, or an overstatement? Then we might look at more contemporary publications? One would be "Germany's future" from 1917 (archive.org).

From that we see the following snapshots:

For a contemporary look at 'Europe', based initially on Septemberprogramm, but with the successes later in the war, the possibilities for a grab of land expanded, a bit:

_{(Src here: Maps from the British Dominions Year Book 1918. Edited by Edward Salmon and James Worsfold. London: Eagle, Star and British Dominions Insurance Co. via Perry-Castañeda Library Map Collection.)}

Remarkably, to label the vast territory, now only the first two letters would fit into the old borders of the Reich…

A pipe-dreamish optimistic way – that was minority position – is recorded in the Imperial War Museum:

Alban Rumann, 1915, Germany. IWM (Art.IWM PST 7215),

In that vision, England is a German colony, Scotland free as an independent kingdom, the whole of France of similar status, but apparently administered from Berlin like Alsace was before 1914, Belgium, northern France as conquered in 1914 and the Baltic region annexed directly. Much of the Eastern Europe hinterland is given to Austria-Hungary though and Poland nominally independent.

Plus: as a direct 'war aim', these colourful maps have to be labeled 'allied propaganda', not entirely accurate.
While German plans really envisioned a quite agronomically oriented expansion into the East, for the state territory itself, most plans were a bit more modest, calling for vast annexations of directly adjacent lands, and a fragmentation of bordering and then in consequence German-dependent states carved up along ethnic lines, according to nationalist thinking, if possible. If not, then 'made possible'.
These exact ideas displayed in the maps from the British Dominion Yearbook of 1918 were not widely shared in Germany.
But these ideas were all on the table indeed, and this question asked for 'long term plans'.

In effect Germany's elites and masses were confronted with the choice, over time, of trying:
(1) to preserve the Small Germany, which Prussia dominated and millions of whose inhabitants, German-speaking or otherwise, were branded as enemies—in short, a basically unstable German situation;
(2) to escape from that instability by creating a Great Germany, with Austria and parts of its empire absorbed;
(3) to go further and seek a German-dominated Mitteleuropa running from the North Sea to the French Alps, from Alsace-Lorraine into Western Russia, and including as at least economic satellites the former members of not only the Austro-Hungarian but the Turkish empires as well.
As Fischer has persuasively argued, Mitteleuropa was the choice that most of the elites for converging reasons came to embrace shortly before 1914.
_{— Michael R. Gordon: "Domestic Conflict and the Origins of the First World War: The British and the German Cases", The Journal of Modern History, Vol. 46, No. 2 (Jun., 1974), pp191–226.}

And that longterm plan was a (middle) European Economic Union, under German leadership.

— Friedrich Naumann: "Mitteleuropa", Reimer: Berlin, 1915. (Note that this is a 'liberal' author! Cf. — Bo Stråth: "Mitteleuropa From List to Naumann", European Journal of Social Theory 11(2): 171–183, 2008. PDF)
— Henry Cord Meyer: "Mitteleuropa: In German Thought and Action 1815–1945", International Scholars Forum 4, Springer, 1955.
— Jörg Brechtefeld: "Mitteleuropa and German Politics: 1848 to the Present", Palgrave Macmillan, 1996.
— Maciej Górny: "Concept of Mitteleuropa", 1914–1918-online, 2015.
— Florian Greiner: "Der „Mitteleuropa“-Plan und das „Neue Europa“ der Nationalsozialisten in der Englischen und Amerikanischen Tagespresse", Zeithistorische Forschungen – Studies In Contemporary History, Heft 3/2012.
— Fritz Fischer: "Hitler war kein Betriebsunfall", Beck: München, ³1993.
— Fritz Fischer: "Krieg der Illusionen: die deutsche Politik von 1911 bis 1914", Droste: Düsseldorf, 1987.
— Fritz Fischer: "From Kaiserreich to Third Reich: Elements of Continuity in German History, 1871–1945" (Bündnis der Eliten: zur Kontinuität d. Machtstrukturen in Deutschland 1871–1945), Allen & Unwin: London, 1986.