Why did the USSR send tanks and militaries in Hungary and Czechoslovakia?

In Czechoslovakia, The Ruler was a friend of the USSR, but he made reforms that the Warsaw Pact did not agree with, He attempted many libertarian reforms so the Warsaw pact with 500,000 troops invaded and put a more friendly government in place. In hungry their was a student protest, and the army fired into the crowd killing many people, so in response the people revolted, and the USSR feared that a successful revolt would put a friendly-US government in place, so the Warsaw Pact invaded and remade the government and crushed the revolt