Wrong!
1) Poland's never invaded Slovakia. You probably meant Zaolzie, which is area around city of Cieszyn - on the Polish - Checholovakian border. In fact - when the Germans entered Chechoslovakia Polish troops took that area over. I'm not proud of it, especially because of the "company" and circumstances in which it happened.
But you should know, that Zaolzie was actually regained by Poland, because it was taken by the Chechoslovakians in 1919-1920, when Poland was fighting the Bolsheviks.
2) I have no idea what you meant writing about Ukraine. Please let me know, so maybe I'll find something new about history of my country.
From this site, on the Russo-Polish War (1919-1921):
After minor conflicts in 1919, in April 1920 a Polish force invaded Ukraine, took Kiev in May. The Soviet Red Army launched a counteroffensive and reached the Vistula near Warsaw in August 1920, where they were defeated by the Poles (Miracle of the Vistula). A truce was signed in September, the Treaty of Riga (March 1921) ended the war. The Polish forces suffered c. 25,000 fatalities, the Russian forces c.105,000.
L,
I think alot depends on how far back we go in considering what "Poland" means.
Before the first partition, weren't portions of Lithuania and Ukraine within what was then regarded as Poland?