What factors and causes leaded to collapse of communism system of Soviet Union and leaded to transition and creation of democratic Russia

Discuss factors and causes why people of Soviet Union wanted to change the communism system into Democratic. Be concentrated on Russia only -How and long on it took to change the regime -what were expectations of people from New Democratic system -why the people of Soviet Union wanted and needed a change. -how people were strangling in 80th and beginning of 90th in Soviet Union under communism system -talk a lot about the transition from communism to democracy (very informant but do not over exaggerate) 2-4 scholarly sources