who should be responsible for the cold war

There are different theories explaining the cold war:

1. Structural realists consider that the dominance of two major powers (i.e. USSR and USA), resulting in a "bi-polar" world structure is the main cause of the Cold War. They argue that such rivalry shaped the two powers to react to each other through different forms of competition, e.g. armament race, space race, etc. in the attempt to out-power the other, thereby increasing the tension between them.

2. Another school emphasises the importance of the fear of nuclear which ended the 2nd World War.

3. Some other looked more on the cultural differences. As the US developed on a capitalise road, the USSR attempted to show that its ideologies of Marxism, Leninism and socialism were more superior.

In sum, it would surely be an incomplete answer trying to say either USA or USSR was more responsible for the Cold War.