How do atomic weapons become a key element of the cold war

Because the past that we have had with atomic energy if one was to impact an area full of heavy population they would all be killed and the blast could be seen from even far away it would create a fallout or nuclear holocaust

The cold war was when countries were all wary of each other and would threaten each other, but the more advanced and the more atomic weapons that one country had available the less likely they were to be attacked. The cold war was mostly a race in who would have to most and who would have the most advanced atomic weapons.