What role did the soviet union play in the rise and fall of the communism in eastern europe?

It was because of USSR that socialism rose in Eastern Europe. Looking for areas of influence they approached these countries that, astounded with the Soviet "wealth" accorded to use this socio-economic system. When socialism began falling, mainly in 1989, it represented not only the decay of the Soviet Union but of socialism as a whole.

P.s. Note that there is a huge difference between socialism and communism. The first one is the state through which a nation has to go through to become a truly communist country, where everything is shared. Also, communism is anarchic. Both are horrible systems but it's important not to misunderstand some basic concepts.