Prussia Annexes Bohemia and Moravia in 1866

I would assume relation between Prussia and Austria will remain hostile and frosty for a long time if this happens.

Might Austria not support the French in the Franco-Prussian War of 1870.

1. I have given some extensive thought to this scenario for a TL of mine since a greater Prussian-Italian success in 1866 was a very important component of the multiple PoD. Certainly acquisition of Bohemia-Moravia, another major industrial region in addition to Rhineland-Westphalia, Silesia, Saxony, and Brandenburg, would substantially strenghten Prussia/Germany,

2. and the German state would be much more capable than A-H to contain the rise of Czech nationalism to manageable levels.

3. As a matter of fact, Germanization of the region would be far from unlikely in these circumstances.

4. In these circumstances, I am rather skeptical A-H would be able to survive (and if it joins France in the 1870-71 war, it would sign its own death warrant, since Italy and Russia would then surely join Prussia),

5. and even more skeptical in this scenario Russia would still join France's side, just for the sake of a few French loans. Germany ITTL would be even wealthier thanks to the resources of Bohemia-Moravia (and in all likelihood, German Austria as well), and entirely able to give Russia all the loans it may want. With Austria gone or hostile to Germany, it very likely Russia would choose alliance with Germany, as long as the guys in Berlin and St. Petersburg do not exceed William II and Nicholas II in stupidity.

6. In this scenario, complete collapse of the Habsburg empire in 1866-71 would be the most likely outcome. Austria would suffer a severe loss in terms of prestige and resources, and the Italians and Magyars would be driven to escalate their own claims to a level the Habsburg empire may hardly survive. Its OTL recovery after the 1859-67 trials (coming on top of the 1848-49 shock) was already a close thing. As a matter of fact, one of the best PoDs to justify this scenario would be a better Italian military performance with a victory at Custoza and Lissa. This was quite doable with a few changes in the Italian chain of command, since the fundamentals of the Italian army were good in 1866 (despite the stereotype) and in no way inferior to Austrian ones, and the OTL defeats were entirely caused by lousy commanders. A parallel Prussian and Italian success would allow the Italians to make greater demands at the peace table (in addition to Venetia, also Trent, Kustenland, and Dalmatia). This in turn would drive the Prussian King and generals to enforce their wish for greater Prussian gains (in addition to Hanover and stuff, also Bohemia-Moravia, Austrian Silesia, and Saxony), overruling Bismarck's preference for a lenient peace.

7. In these circumstances, the Habsburg empire would in all likelihood collapse; the Magyars were restive in the 1860s and their consent to the Ausgleich compromise was difficult to obtain. If the Habsburg perform worse in 1859-67, odds are the Hungarians would deem the dynasty a lost cause and rise up again in rebellion, and nobody would be able or willing to stop them after a military disaster. If anything, Russia is likely to intervene and annex Galicia and Bukovina, to grab its own share of the Habsburg spoils and prevent the rise of a Polish irredentist haven. After Austrian ingratitude in the Crimean War, the Tsar had no wish to save the Habsburg again, Russia had a pro-Prussian stance after the two powers cooperated to suppress the January Uprising, and the Russians had much to gain from a free hand in the Balkans if Austria collapsed. In these circumstances Grossdeutchsland unification of Germany under Prussian leadership would be inevitable due to irresistible pressure of German nationalism, notwithstanding any anti-Catholic misgivings of the Junker elites. Bismarck would just have to adjust his plans for unification accordingly.

8. Even if by some political miracle Austria does not fall in 1866-67, its survival after this humiliation would in all likelihood drive the vengeful Habsburg to join the Franco-Prussian War on the side of France. Most agents and observers at the beginning of the war expected a French victory, so the Austrians may be easily tempted and misled to expect an easy revenge thanks to French military power. However, an Austrian intervention would surely drive Italy and Russia to side with Prussia (Russia had signed a secret treaty to guarantee its intervention if Austria sided with France). Such an enlarged conflict would inevitably cause the utter destruction of Austria.

9. I'm rather skeptical in this scenario German annexation of A-L would be avoided, since there were sound ethnic-linguistic, historical, economic, and strategic reasons for it that greater Prussian success against Austria would not invalidate. A-L was a German-speaking and historically German land that the French state had forcibly acquired from the HRE at the moment of its greatest weakness, it was quite valuable economically, and rather useful strategically to protect the Rhineland from the French invasions of Germany that historically were the norm before 1870.

10. Moreover, it is quite likely Italy would join Prussia in the war and make its own territorial demands at the peace table (Nice, Corsica, Tunisia, Savoy). This would make even less acceptable for Germany to give up A-L. As a matter of fact, it is likely a greater Prussian and Italian success in 1866 would make both powers less willing to appease Napoleon III on the Luxemburg and Rome issues. Tensions with France would escalate and the 1870 war would occur earlier, include Italy, and have a different, double casus belli rather than the Spanish succession. This would allow Germany to annex Luxemburg, too.

11. Last but not least, in this scenario it is quite likely Europe would see the formation of a stable alliance between Germany, Russia, and Italy thanks to compatible strategic interests after the demise of Austria. As the OTL Axis showed, Germany and Italy may easily and gainfully cooperate as partners if A-H is not in the way. If the Habsburg empire collapses, one of the best ways for Germany to manage Russia is to support its expansion in the Balkans and the Near East against the Ottomans. After the Russo-Turkish war, the Russians may easily make greater gains at the peace table if Austria is no more, Berlin and Rome support St.Petersburg, France is still weakened by defeat and postwar instability (going to be worse if they took a beating and lost stuff to Italy too), and Britain is thus isolated. This would secure Russia as a loyal ally for the German-Italian bloc and allow Russian ambitions to be fulfilled in a way that does not threaten its interests. Of course, this alignment would inevitably drive the formation of an Anglo-French-Ottoman Entente sooner rather than later, but the Eastern Powers alliance would always be the strongest side in a *WWI (short of America joining the Entente from the beginning) and land trade across Central Europe would make it effectively immune to Entente blockade. In this context Germany would have relatively little to fear from a vengeful France.

12. Broadly speaking, this kind of PoD is rather likely to lead to the early collapse of Austria, a greater success of Germany, Italy, Russia, and Hungary (it would become a client state of the EP but keep most of its traditional lands, except possibly Croatia), and more trouble for France, Britain, and the Ottoman Empire during the late 19th century and early 20th century.

13. This in turn may cause the more successful countries to experience a nicer and less troublesome political course and more economic development, while the more troubled nations may go down a nastier path (e.g. by becoming the birthplaces of fascism or communism; in my TL, postwar France and later the Franco-Iberian union it creates become the main stronghold of *fascism). Poland and the other subject nationalities of the Russian Empire would likely never regain independence if Germany and Russia remain strong and friendly. The Czechs would likely become a later analogue of the Sorbs, and the map of the Balkans would be substantially different (in my TL, the region gets divided between Greater Hungary, Greater Croatia, pre-1914 Romania, a Serb-Bulgarian *Yugoslavia, Italian Albania, and Greater Greece). It is quite possible the example of completely successful German and Italian unifications since the 1860s may improve the chances of other historically incomplete or missed national unifications, such as Scandinavia, Iberia, Greater Netherlands, or even a non-Nazi, HRE-sized Greater Germanic Reich.