"Aggressor" is a fairly political and loose term. I believe they were both proportionally bad in the situation. However since you are likely looking for an argument for one side, I suppose I would have to go with the USSR. They started the Berlin blockade which both violated treaties and nearly led to a large war. At the time in Russia, if anyone disagreed with their secular agenda or government they would be exiled. I think it's important though to again point out that contrary to popular belief, both sides got into unwanted wars and did aggressive things during the time and neither should be dubbed the only "aggressor"
