Poland comprises, more or less, pre 1939 Polish borders, plus a deal of OTL Belarus.
Recreated after the First Great War, Poland was one of the main targets of both the Third Reich and the Soviet Union, and the Nazi invasion of Poland was the detonator to the Second Great War.
After the Russian invasion of eastern Poland and the surrendering of the Polish government to the Germans, officially Poland ceased to exist, according to German and Soviet authorities. Nazi Germany begun a process of Germanification, while the Soviet Union annexed eastern Poland as part of the Soviet Socialist Republic of Bielorussia.
The Reich agreements with the Nationalistic government in Russia set in St Petersburg in Octuber 1942; demanded that Ukraine and Bielorussia were not part of Russia, and therefore fair game for Germany.
However, despite all efforts to suppress the polish language and culture, and the attempts to make former Poland more German, the Nazi regime required the Poles and other Slavs to survive as second class citizens, providing cheap labour. The Polish identity was never suppressed.
Politically, however, Poland disappeared. Parts were incorporated to existing German states, parts were created as new states that did not recognized recent history, but rather obscure historical or mythical German names.
In March 7, 1986, the governors of Baviera, Lower Saxony, Netherlands and Prussia sign a declaration banning the National-Socialist Party and declaring the end of the Third Reich. The declaration is adopted by separatist leaders in Poland, Denmark and Ukraine.
The signation of the democratic constitution of Germany on September 9th 1986, gives Poland her independents back. However there was a question of what was meant as Poland by this time. Basically a puzzle of territories that should include Varsovia and Cracow, and territories with still some important Slav population in the northwestern Reich were composed as Poland. This new Poland included, more or less, Poland before 1939 except for some bordering and highly Germanized areas such as the Danzig corridor, plus the former Bielarussia.
The new Poland was now a mixture of ethnic Germans, Poles and White Russians, among with Czechs, Slovaks, Russians, Danes, Dutchmen, and several other nationalities. Those cataloged as Arians during the Nazi regime were by far better educated than the Slavs, and already formed a dominant social class. Most of them only spoke German, and few could communicated in Polish. On the other hand, the ethnic Poles wanted a revindication of years of oppression by the Germans.
Despite the efforts of the German kingdom to protect her fellow Germans, the Polish revindication parties were dominant in the establishment of the new Republic of Poland and the short lived constitution.
In 47 years of occupation a large group of the Polish population (mostly Arian and ethnical German) are grown up with National-Socialism. This resulted in some extreme National-Socialist Groups. On April 5th 1987 one of these groups the League for a National-Socialist Poland (LNSP) forced a coup d'etat. Erich Krüll, a 42 year old ethnical German, is placed as President and Führer of the Republic of Poland.
Germany on road to democracy directly cuts off ties with Poland. More Eastern European states followed and forced the Krüll government into an almost isolation.