1) Living conditions: Living conditions were hard, as many famiilies didn't have anything special (they worked pretty much the same, in the fields or in factories and such). Food were eaten in a big ol' room, and they usually slept in a large house. Living conditions became worse and worse as time grew on.
2) Mistreatment: Many citizens felt that they were mistreated and that they didn't have enough rights, and so they tried to protest. Of course that was knocked down, and so they were all the more angry.
3) Help from the NATO and US; As the US promised satellite nations of USSR that if they broke away, they would be able to enter into the Marshall Plan (a plan that lent money too countries to help them rebuild) Because USSR really didn't help their satellite nations much in a way, many broke away to try to rebuild both their country, political system, and the way they run things.
hope this helps