what are three major events, ideas, or poicies that contributed to the end of the soviet Union? including something about easern europe!

help pleaseee!!

http://en.wikipedia.org/wiki/History_of_the_Soviet_Union_(1985%E2%80%931991)

http://www.soviethistory.org/index.php?action=L2&SubjectID=1991end&Year=1991