text: The U.S.S.R. was involved because they were the main enemy to the U.S. in the Cold War (1945- 1990). Understand that the U.S.S.R. helped the Allies out in WWII, and at the Yalta conference with Winston Churchill, and FDR, they all decided that the smaller countries such as Poland (invaded by Nazi Germany) and Czechoslovakia would decide how they wanted their government to be. The U.S.S.R didn't keep this promise, and these countries became communist.