Germany could remain a relatively large block somewhat resembling its pre-war shape in terms of international borders. But that does not mean these borders and the block itself weren't challenged. Most of the rebellions in Germany at the end of the war were communist uprisings, often quickly put down by proto-Nazi troops, which were officially and originally ordered to quell nationalist uprisings on the fringes of the Reich, mostly Polish incursions.
That is the first difference compared to Austria-Hungary: Austria was a weak state – structurally and administratively – before the war and really already in complete shambles by the end of the war. Many centrifugal forces – active from before the war – and utter breakdown across the field. Czech autonomy, only hinted at in Wilson's 14 points, was rapidly expanded into full independence by Czech nationalists while the Austrian leadership still tried to woo the Czechs into participatory citizenship.
Meanwhile Germany remained an orderly state, crushing any dissent and aspirations, with a self-image of "undefeated in the field" with functioning and effective (para-)military units. The ruling elites (except for the monarchs), the civil service and military power structures were a little shaken, but otherwise left completely intact. With the help of the social democrats in gunning down any rebellion the same conservatives loyal to the fatherland with their imperial ambitions were not only able to survive but emerge from the turmoil only strengthened.
The politics of nationalism are and were a complete disaster on every front imaginable. And arguing with nationalism as an intrinsic factor for anything is falling into the trap that the propagandists of nationalism laid out all around. Nationalism is a construct of arbitrary imprecision, actively invented and absent from human nature, but apparently useful for the ruling elites. (Cf. Immanuel Wallerstein: "The Modern World-System IV: Centrist Liberalism Triumphant, 1789-1914", "Race, Nation, Class: Ambiguous Identities", "Studies in Modern Capitalism: Geopolitics and Geoculture")
Its major political problem was twofold: how to provide historical legitimacy for the Bismarckian (Prusso-Little German) version of unification which had none; and how to deal with that large part of the democratic electorate which would have preferred another solution (Great Germans, anti-Prussian particularists, Catholics and, above all, Social Democrats). (Hobsbawm)
The "nation" of Germany (really the second Reich) was forged by Bismarck just a few decades before and explicitly excluding the Germans from Austria, for practical power politics reasons. But including the Danes and Friesians in the North, the Sorbs and Wendish in the Middle, a few French in thoroughly Germanic Alsace-Lorraine and Poles, Kashubs etc. in the East. Even the ever separatist Bavarians. As well as the 30% Polish minority in the industrialised Rhineland.
But for French revanche, Europe might have faced the Eastern Question with comparative ease. What gave the impending crisis its dreadful character was the fear of a simultaneous Franco-Russian assault on Central Europe. No American saw the essentially tragic nature of the Franco-Russian alliance more clearly than did William R. Thayer, an acute observer of the European scene, who wrote in November 1891:
Russia is ... the center of the warlike storm-area to-day. Eliminate her from European politics, and the other powers would have no plausible excuse for keeping up their armaments, because France, in spite of her grievances and wrath, would see the hopelessness of dashing her head against Germany, supported by Austria and Italy. The possibility of winning Russia as an ally ... has forced Germany to stand by her guns. But the Russian monster threatens not only Germany; as Napoleon discerned eighty years ago, he endangers all western Europe.
With the approach of peace, Wilson’s immediate challenge lay in Europe, where his leadership hinged on an armistice based on his Fourteen Points. The President understood fully that the European Allies did not share his vision of the post-war world, especially after the Russian publication of the Allied secret treaties. To protect his diplomatic independence, Wilson rejected a formal alliance with Britain and France, designating the United States officially as an “associated power” in the Western coalition. Throughout the final months of the war, he refused to compromise his principles by recognizing the secret treaties, or to prejudice any post-war Allied negotiations with wartime concessions to known British and French interests.
Those partitions away from the former Reich's territory clearly prove that the 14 points of Wilson's address were moot when the armistice was signed. They served their purpose and were put to rest. While some of the concepts of national self-determination were publicly proclaimed, in practice they were way too often undermined or ignored. Gerrymandering of voting districts in Schleswig, Eupen, Malmedy, parts of Eastern provinces, Saar and Alsace cut off without a vote, Rhineland occupation, relatively open voting fraud in other areas are a contestable issue. Later actions on behalf of the allies in forbidding German-Austria to join the other Germans and the ethnic make-up or construction of Czechoslovakia expose the best-before date of the principles of the 14 points.
Nationalism as well as "self-determination" are good for rousing peasants and middle class voters who didn't care before (as evidenced by peaceful co-settlement patterns). When it comes down to actual decisions: power and economic interests rule the day, any day.
Splitting up a country that was only formed a few years before was easy. Napoleon did just that a hundred years before with German lands:
An exercise that after World War II was done again, of course.
And after World War I it was not unimaginable to separate especially Rhine-provinces and Bavaria from the Reich. Bavaria had to be bribed into the union from the start. The Rhenish resented Prussian rule, were catholic and had separatist tendencies, leanings and sympathy for the French who furthered their independence movement, occupied the zone in question for a time. They Rhenish and the Bavarians resented and still resent to a degree the Prussians. And they speak another language too:
Notice the fat colourful lines that cross ancient, 19th, 20th century, and present day borders. Even today people from both sides of the border between Germany and the Netherlands understand each other much better than Bavarians can understand Friesian people. Swabians today advertise jokingly their inability to speak proper standard high German.
Calling Germany a more homogenous country is quite misleading. A Germany based on ethnicity according to nationalism would incorporate much more of the Netherlands and Belgium, Switzerland, Bohemia and the whole of Austria. But going by linguistic borders alone could arguably also lead to splitting Germany into several pieces, since East-Netherlands and Northern Germany as well as Bavaria and Austria are in two separate but very smooth continua. Culturally, language is not the only divide to observe. Even religiously German speaking countries remain split – or perhaps more accurate: very thoroughly mixed up:
So the second main difference between Germany and Austria-Hungary is that Germany could have and should have been dismantled much more. But the French were not allowed to have it their way. Nor the Polish or the Czech were allowed to have it all their way by the other powers. Not because of anything about language or nationality or self-determination. Those concepts only mattered in rhetoric not in actual aims, plans or interests.
The French negotiating claims against Germany were presented to the British and Americans in the opening stages of the peace conference. For clarity of exposition, they may be divided into territorial, economic, and security elements, although this division obscures their interconnectedness. Although the French had claims on Germany's African colonies in the Cameroons and Togoland, the territorial starting point within Europe must be Alsace-Lorraine, the province and a half that in 1871 they had forfeited. The Clemenceau government successfully insisted that it be allowed to regain Alsace-Lorraine without a plebiscite, and with the authority to expel German immigrants and liquidate German holdings in mining and heavy industry. The protection for minorities that qualified other territorial transfers decided at the conference did not apply here. The northern frontier of Lorraine, however, had changed on many earlier occasions, and Clemenceau asked not for the line of 1870 but that of 1814-15, which included two salients round Saarbriicken and Landau. The former would give him most of the Saar coal basin, but he also wanted to occupy the remainder of the coalfield situated beyond the 1814 line, to exploit its mines and to incorporate the whole of the Saar into the French monetary and customs zone. Farther to the north lay the German territories on the left bank of the Rhine, which the French contended should be divided into one or more nominally independent states, to be disarmed, made neutral, and given their own central bank and note issue. They would be included, however, in the "Western European customs zone," and both the left bank and the Rhine bridges would remain indefinitely under Allied occupation.
Should this program be rejected, Clemenceau and his advisers intended to demand the annexation of a glacis inhabited by one million Germans to the north of the 1814 frontier.
This security system would be incomplete if it excluded the Low Countries, and the French hoped for military cooperation with Belgium, as well as closer economic integration. They supported Belgium's territorial demands on Germany and its pretensions to territory from the Netherlands, which latter would be "compensated" at Germany's expense. In Luxembourg, however, which the Belgians hoped to annex, the Clemenceau government refused Brussels a free hand. The Versailles treaty confirmed Luxembourg's departure from its prewar customs union with Germany but transferred the Grand Duchy's principal railway system from German to French control.
In the remaining territorial questions, French policy moved to weaken Germany as much as possible, disregarding both a scrupulous adherence to self-determination and sometimes the wishes of Germany's neighbors: Denmark, for example, wanted less of Schleswig than Paris wished to see assigned to it.
Similarly, France denied the legitimacy of Austrian aspirations for union with Germany, and the peace treaty required the Germans to respect Austrian independence in the absence of a contrary decision by a League of Nations in which France would have a veto. The new authorities in Prague, by contrast, wished to maintain control over the German-speakers of the Sudetenland, and as early as June 1918 the French had publicly supported the Czech National Council's desire for independence "within the historic limits of your provinces." The French conference delegates agreed that the Sudetenland was strategically and economically indispensable to the Czechoslovak republic and fended off American challenges to Czech claims on it.
In September 1918 Clemenceau had made a similar public promise to the Polish National Committee that "on the day of our victory … France … will spare nothing in order to revive a free Poland corresponding to the latter's national aspirations and bounded by its historic limits." These limits the French Foreign Ministry understood to be the Polish frontiers of 1772, giving the country a broad land corridor to the Baltic at Germany's expense, as well as the port of Danzig. During the armistice negotiations the ministry tried unsuccessfully to stipulate that German forces should retreat behind the 1772 frontier, and an interdepartmental meeting on January 29 reaffirmed support for a strong Poland with a broad land corridor as a "buttress against German expansion," although the "internationalization" of Danzig and the corridor might, in deference to Britain and America, have to be accepted as a second best. Farther to the south, in contrast, the French supported Polish claims to the whole of Upper Silesia, which contained the second largest German coalfield, and, although of mixed population, had not been part of Poland in 1772.
To territorial amputations would be added economic restrictions. […] If the wartime inter-Allied agreements for pooling raw materials could be preserved, it would demand only reparation for the damage in the occupied regions, together with protection against dumping and other unfair trading practices. But in the absence of such agreements it would seek an "enormous" German debt burden, as well as coal deliveries of up to 35 million tons annually for twenty-five years. If combined with Germany's loss of the iron ore, coal, and steel of Upper Silesia, Lorraine, and the Saar, such terms would place its heavy industry at a lasting disadvantage and go far to redress the Franco-German imbalance that had grown up in the prewar years. […]
Both the territorial and economic elements of the French position, then, had strategic implications. They must be considered in conjunction with the Clemenceau government's wider security demands. It did not ask that Bismarck's work be undone and German unity broken up, although it encouraged Rhenish and Bavarian separatism and unsuccessfully challenged the Weimar government's legal authority to sign the Versailles treaty.
In contradistinction to American thinking, such a body would be a disguised continuation of the wartime coalition, and in the Chamber of Deputies on December 29, 1918, Clemenceau served public notice that he still saw value in the defensive system, now condemned by "certain high authorities," of strategic frontiers, armaments, and alliances. Nonetheless, his "directing thought" in the negotiations would be that "nothing must happen which might separate after the war the four Powers that were united during it. To this unity I will make every sacrifice."
At one stage the French wanted apparently to achieve something like this:
or more colourful:
Germany went into the shape of borders it had after 1919 because the unchanged from before elites of Germany still aspired to a Great Reich (and after crushing the revolution and seperatist movements had the means to do so) – and Americans and British were able to restrain the French (and some other minor neighbours) from taking what they wanted.
Michael S. Neiberg: "The Treaty of Versailles. A Concise History", Oxford University Press: Oxford, New York, 2017.
Norman A. Graebner and Edward M. Bennett: "The Versailles Treaty and Its Legacy. The Failure of the Wilsonian Vision", Cambridge University Press: Cambridge, New York, 2011.
Manfred F Boemeke, Gerald D. Feldman and Elisabeth Glaser : "Treaty of Versailles. A Reassessment After 75 Years", Cambridge University Press: Cambridge, New York, 1998. (Review)