Why was cold war such a threat to a world peace?

The two biggest powers in the world did not trust each other and looked at their interests in Europe in particular and their build up of nuclear weapons as major issues. The Soviet Union had extended its influence into eastern Europe, setting up a communist bloc. This was seen as a threat. They both had nuclear weapons. They were both increasing their stocks and doing other things to build their power, like in the space race. There were some serious issues, like in the Cuban Missile Crisis, which nearly caused conflict.