[bravo whiskey]

As for Russia the Poles invaded Russia as soon as they became a country in 1919-1920.

[Cronos]

that's not really true. In 1919 the Tsarist empire, German empire and Austro-Hungarian empire collapsed. Basically the entire area from the Rhine to Vladivostok was a free-for-all.

The USSR wasn't a successor state to the Tsardom.

Polish, Lithuanian, White Russian, Bolshevik, Ukrainian etc. groups all fought to create homelands for themselves

The Western Entente decided the western borders of Poland, but the east was a free for all