The Russian Empire (or an early Soviet Union that conquered Poland) annexes Germany for 70-80 years so that Germany and Poland are both oppressed and at equal standing. When the Russian sphere collapses, all the non-Russian states break off and unify into one bloc which is basically a German-Polish Union marked by its two largest members, but also includes the Baltic states.
In OTL the end of Soviet domination has hardly produced a movement for unification into one state in eastern Europe. (Yes, some of the nations have joined or want to join the EU, but that is something quite different.) Indeed, the actual result has been that even peoples as akin as the Czechs and Slovaks found that they no longer desired to live in a single state. The Poles, had they been incorporated into the USSR (with or without the Germans) and then liberated, would have no desire to enter a purely German-Polish union--even with the Baltic states added, it would obviously be dominated by Germany.
(By the way, I doubt very much that in a Soviet superstate including Germany, the Germans would be oppressed in a
national sense. On the contrary, they could very well be the dominant power within the Union or at least equal to the Russians. But such a state is very unlikely to come about anyway--Stalin was very much opposed to it, as I indicate at
https://www.alternatehistory.com/fo...-all-of-the-warsaw-pact.464098/#post-18636109 and was even accused by Lenin of "nationalism" and "chauvinism" for viewing the incorporation of even Poland, let alone Germany, into a Soviet federation as impractical. As for the Russian Empire conquering all of Germany and annexing it, this was never a serious possibility. A lot of Russian nationalists though that Germans were already too influential in Russia!)
The only kind of German-Polish union possible would be one with a German prince at the head of a puppet "Kingdom of Poland"--or, still worse, the kind of "union" Hitler produced...
