Answer
The fact that both the United States and the Soviet Union had atomic weapons shaped the progress of the Cold War by fueling an arms race between the two countries. This led to the development of more powerful and destructive weapons, including hydrogen bombs, and the concept of Mutual Assured Destruction (MAD), where both sides knew that any nuclear attack would result in the destruction of both countries. This led to the policy of massive retaliation, where any attack on the United States or its allies would result in a massive nuclear response. Brinkmanship, or the willingness to go to the brink of war to achieve political goals, also became a common tactic. Overall, the possession of atomic weapons greatly increased tensions between the United States and the Soviet Union during the Cold War.