How was a balance of power established between the US and the Soviet Union

The balance of power in the Cold War was mainly kept through the development and possession of nuclear weapons. There was practically an arms race between the United States and the Soviet Union for most of the Cold War era.

Nevertheless, the development of nuclear and other types of weapons of mass destruction was not meant to actually prevail in a hypothetical war, but to deter the rival superpower. A strategic military doctrine was adopted then: mutual assured destruction, or MAD. The MAD doctrine held that the probability of being destroyed by enemy nuclear strikes was a deterrence factor that forced the two superpowers to coexist.