[avodonosov]

> the land that was historically eastern Poland isn't part of Russia now -- it's part of Ukraine and Belarus

The Belarussian / Polish border today is almost exactly the border between Kingdom of Poland and Grand Duchy of Lithuania within the Polish–Lithuanian Commonwealth. So "historically eastern Poland" is not right there. Some like to think of the whole Commonwelth as Poland, which really dominated there. But in this case whole Belarus and Ukraine are "eastern Poland".

That's what poles tried to restore when got chance to recreate their state after WWI, as I understand. The full commonwealth. But only got to the borders we know as the pre-1939 Poland.

BTW, Ukraine is mostly the part of the GDL annexed by the Kingdom of Poland during the Union of Lublin. The todays Belarus / Ukraine border goes by this line.

There are overlap maps in wikipedia: https://en.m.wikipedia.org/wiki/Polish%E2%80%93Lithuanian_Co...

Going deeper in history of GDL, Russia and Poland uncovers more.