Imagine Habsburg Monarchy, but extending to more-or-less entire Germany and without the Austro-Hungarian Compromise (so it is more in the vein of pre-1867 Monarchy).
This is automatically the enemy of France, Britain and Russia. Habsburgs are less of a direct "troublemaker" than the Hohenzollerns, but the fact that they unite such a vast realm under their aegis makes them threat #1 for all other parties.
If you want a workable solution, you probably have to wrangle the early ambitions for unification into working out
just right
.
Even then, I think -- as
@gral notes -- that the most probable outcome is that there will be earlier "European wars" as a result. However, these wars can realistically be prevented from being world wars. In essence, you'd see smething more akin to the Crimean War and Franco-Prussian War, but on a larger scale. These would be the equivalent of the world wars (i.e. a first war, and then a later "re-match"). However, while these would be larger in scale than those OTL counterparts, they wouldn't be world wars... and they'd be fought before the innovations that made the world wars so massively deadly.
The issue with a "super Habsburg realm" is that it is so massive that its enemies can never relax until it is broken. But a "Greater Germany" that spins off the non-German Habsburg realms under cadet branches... that kind of power can forge foreign alliances and subsequently win the ensuing "European wars" of the 19th century.
Plausibly resulting in general peace afterwards.
The set-up for the scenario I have in mind would be as follows:
-- The greater German solution is embraced in the wake of 1848, under Habsburg leadership.
-- The "German lands only" vision must prevail, and the "all Habsburg lands included" vision must be rejected from the start. The non-German Habsburg lands must, from the start, be set to become separate states under Habsburg cadet branches. (This issue was
the biggest obstacle to Habsburg leadership in uniting Greater Germany.)
-- The Habsburgs must be willing to work with the Russians to permanently settle all open questions regarding Eastern Europe. A willingness to creatively swap a few territories so as to enure future stability is a must. (This matters because if war is to happen, you want it to happen ASAP. Basically: you want a Crimean War where Greater Germany sides with Russia, and their side wins decisively.)
-- The Habsburgs have to humiliate and sideline the Hohenzollerns in a big way in the period 1848-1853, so that Prussia is unable to make a fuss. (Either during unification, or during the upcoming war.)
-- The Habsburgs should divest themselves of their Italian possessions. The optimal strategy would be to sell them to the Sardinian monarchy, in exchange for alliance and good will in the future. (This will keep Sardinia from being an enemy in future wars.)
The actual formation of Greater Germany, and surrounding events, would entail the following:
-- All German lands, plus Czech and Slovene lands, and (actually Croatian-majority) Sankt Veit am Flaum, are united under the Habsburgs. (Except for German-majorty parts of Schleswig-Holstein and Elsaß-Lothringen.)
-- Hungary becomes a separate kingdom under a Habsburg cadet branch. (The German-speaking border strip is to be annexed by Greater Germany first.)
-- Croatia becomes a separate kingdom under a Habsburg cadet branch.
-- Galicia, Bukovina, and the Polish-majority border regions previously held by Prussia are turned into a special administrative territory run by the Habsburg Emperor (but which is explicitly
not part of Greater Germany).
-- Italian holdings (
not including Südtirol and Sankt Veit am Flaum) are sold by the Habsburgs to Sardinia, which in return becomes their ally. (They no longer have any real conflict of interest, and in fact, Sardinia becomes the Habsburgs' favoured Italian contender.)
It's quite realistic that an ATL Crimean War is subsequently won by Greater Germany and Russia, based on secret negotiations beforehand, resulting in join operations and a clear plan for post-war steps to be carried out. Conceivably, Sardinia could even be swayed to join
their side, in return for getting (a good chunk of) Albania, and (more importantly) Corsica at the expense of France.
The post-war settlement would then be as follows:
-- France to give up the German-majority parts of Elsaß-Lothringen (i.e. most of it) to Greater Germany.
-- France to give up Corsica to Sardinia
-- Kingdom of Croatia to be expanded to the Bosna river.
-- Meanwhile, the regions East of the Bosna river and South of the Sava river to become the Serbian Kingdom, under a cadet branch of the Romanovs. This to include Montengro, Kosovo, and most of North Macedonia.
-- Croatia and Serbia to engage in some population swaps, and (no doubt) some unprompted ethnic cleansing of muslims.
-- Wallachia, Moldavia, Bessarabia and Northern Dobruja to form the Kingdom of Romania, under a Romanov cadet branch.
-- Bulgaria to be made into a kingdom under a Romanov cadet branch.
-- Albania (minus the strip taken by Greece) to be annexed by Italy. The removal of muslims to be heartily encouraged, and the country to be placed under the complete control of the Catholics.
-- Greece to be embiggened as much as possible, and recognised as being in the Romanov sphere of influence. (My thinking is: OTL modern Greece + Northern Epirus + a bit of North Macedonia + all of Thrace + Ionia + Cyprus.)
-- Constantinople and the Straits to become a codominium with guaranteed free trade access for all the countries on the war's winning side. To be administrated by Greece and Russia jointly.
-- Russia to annex all previously Turkish-held Armenian regions.
-- A Pontic Greek province under Russian overlordship to be carved out.
-- Turks to be expelled from all the aforementioned regions, and none too gently.
-- Galicia to the East of Lwów (Lviv), as well as Bukovina, to be ceded to Russia by the Habsburg Emperor.
-- Polish-majority lands held by Russia to be ceded by Russia to the Habsburg Emperor. These lands, and Western Galicia up to and including Lwów, and Polish-majority lands formerly held by Prussia, to be united into the Kingdom of Poland under a Habsburg cadet branch.
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What I have outlined above may very plausibly result in another war later in the 19th century, but the French and British have no real hopes of winning that war. The alliance of Greater Germany and Greater Russia (and their respective spheres) is set up to be remarkably stable, and very hard to bring to its knees.
Once they win this second "European war", presumaly due to their enemies facing exhaustion, I could see Greater Germany annexing Schleswig-Holstein, and maybe Luxemburg. That kind of thing. But basically, after that, the state of affairs is largely settled. When it becomes obvious that German hegemony in Europe is something you can't just undo, and that trying is ludicrously costly, and that the Habsburgs have no further expansion plans (let alone massive naval expansion programmes)... well, the British will stop wasting massive resouces on attempts to break the Habsburgs, and will instead focus on outperforming everyone else economically with their vast colonial empire.
Some further considerations:
-- As the Ottomans get crushed in the ATL Crimean War, Sa'id of Egypt no doubt sees his way to realising his father's ambitions. He becomes the ruler of a realm encompassing Egypt, Sudan, the Levant, (greater) Syria, and the Western half of the Arabian peninsula. (He was a great friend of France, and the political situation here probanly means that the French get to start on the Suez canal a few years earlier.)
-- At the same time, Persia has a chance to try for overlordship over all Kurds, over the Shi'a Arabs of Mesopotamia, and to some extent over the Eastern half of the Arabian pensinsula.
-- Sardinia will still unite Italy, but this time with Habsburg
support. Italy will presumably join the alliance of Greater Germany and Russia, imagining itself to be an equal partner in this triune set-up (but will in reality be a very junior partner that just follows the other two).
-- France will initially be bitter, but through alliance with Greater Egypt, can secure great influence for itself in near-by regions of North Africa. Eventually, they'll control all of North-Western Africa (in the process denying Italy a foothold there). We might also see a French protectorate over Greater Somalia (again, with the Italians locked out, while the French have free access through the Suez).
-- Britain will lose far less in the 19th century European wars than it did in OTL's 20th century world wars. As a consequence, the British Empire is in a far better position, and will remain in that better position for much longer.
-- With Russia dedicating its focus to European affairs ("Finally, Constantinople is in Orthodox hands again!"), their attention to Far East will be correspondingly diminished. You can't be everywhere at once. This means no Russian ambitions beyond Vladivostok, and consequently no war with Japan.
-- The Habsburgs have show very little interest in colonial empires, so Greater Germany will presumably not get involved in that. Britain and France can squabble over who gets the bits that Germany got in OTL.
-- Not much chance of significant Greater German involvement in China, either. At least not in China proper. Again, Britain and France can be the contenders there... along with Japan.
-- Which may spawn a situation where Britain and France put Japan in its place early on. ("Don't get uppity, dwarf state.") As a result, the Japanese hold over Korea may be butterflied entirely, and Korea may instead become a client of France or Britain.
-- Russia (possibly with Greater German economic backing) may be interested in functionally annexing Mongolia, hoping to get resources out of it.
-- All of this greatly reduces the possibilities for the USA to start throwing its weight around. A version of the Spanish-American War may still happen, or it may not. But Japan will be the Anglo-French back yard, and America won't be invited to play a role of real consequence. ("Our gunboats are bigger. Sod off.") In fact, I suspect Britain would nab up the Sandwich Isles (a.k.a. Hawaii). And the USA getting involved in the Philipines will be right out. So any American ambitions will have to be turned towards the Caribbean, Mexico, and possibly other parts of Latin America.
-- The alliance of Greater Germany and Russia will likely prompt the Scandinavian countries to cozy up to each other right quick. Especially if Denmark sides with Britain against the Germans and loses Schleswig-Holstein for its trouble. This Scandivanian block will probably go for formal "armed neutrality", but will in reality side with Britain and against Greater Germany and Russia.
