Why you always forget about this part of the history? I guess it's not illustrated well in your media blaming Russia for all of your miseries.
Certainly not by USSR. By the time USSR took their territories back - are you still forgetting, that Poland had conquered their territories mere 20 years earlier? - Poland didn't exist anymore and the Polish government was in exile in Romania. There was nothing to conquest. USSR took back what was taken from them.
And let's not forget that Pilsudski government, while it lasted, was fascist, just like the Germans. They played a game and they lost. Unlike Austria and Czechoslovakia, which were also thrown over the board for the Germany, they were not innocent here and had their own imperial ambitions (did you forget that they took their part in partitioning of Czechoslovakia, just months earlier?)
Seriously, go read some books about WW2 and stop making fool of yourself in the public.
September 1: Germany invaded Poland
September 17: USSR invades Poland.
- (1917-19) Curzon line, establishment of second Polish republic, establishment of Soviet Union, succession of Russian Empire & impact of Brest-Litovsk treaty, succession states of Austro-Hungarian Empire;
- (1918-21) Polish-Soviet War, Poland annexing Soviet territories east of Curzon line;
- 1925, publication of Mein Kampf; outlining geopolitical ambitions of Germany
- Intermarium project, Jozef Pilsudski, geopolitical ambitions of Poland
- Polish relations to Germany in 1930s
- (1938) Munich agreement, role of Poland
- August-September 1939; pay particular attention to timeline of exile of polish government officials, compared to "USSR annexes Poland".
But of course, you can ignore all that and pretend that USSR had a capability to start a war at the time (hint: they barely defended themselves, it was huge diplomatic effort to stall the attack on USSR till 1941).