Western allies have sold Poland in Yalta.
They didn't "sell". They simply did what was best for them. Going to war with the USSR over Poland was not on the list.
BTW, Mr. K, going to war with Russia over Poland today is not on our list, either. So my personal advice to you is (1) to be nice to Russia, and (2) print that Article 5 and wrinkle it to make it usable when you go number two.