Soviet Union. More than 1.5 million Poles taken prisoner by the Red Army were deported to the Gulags: 760,000 would soon die in Russia, mostly children, who accounted for a third of those deported. Another 22,000 were murdered with the express intent of completely eliminating the Polish ruling class, particularly all officers (and the Katyn massacre was part of the same strategy, initially blamed on the Nazis, but later recognized as entirely Soviet in origin). The remaining Poles, on Stalin’s orders (who would regret having eliminated all the officers), a few years later went on to form the Second Polish Army Corps, which, after a thousand vicissitudes, would assemble in the south of the USSR, cross the Caspian Sea on cargo ships, be trained in Iran by the British, be transferred to Palestine, then to Egypt, and finally embark for Italy, where they would fight and win the Battle of Monte Cassino, take the port of Ancona, and finally Bologna. They were then unable to return to Sovietized Poland, ending up mostly in England, but also in the United States, Italy, and so on.
