How did the atomic bombings of Hiroshima and Nagasaki affect the Cold War arms race?

The atomic bombings of Hiroshima and Nagasaki did not initiate the arms race; rather, they occurred within a context where the Soviet Union had already begun its own atomic program in 1943. While the bombings were primarily intended to compel Japan’s surrender, their existence fundamentally altered the Cold War by establishing nuclear weapons as central to superpower rivalry.1234

The bombings affected the arms race in several key ways:

• End of the U.S. Monopoly: The U.S. initially held a nuclear monopoly, but this was short-lived. Once the Soviet Union conducted its first successful test in 1949, the "rules" of the game changed, forcing the U.S. to shift from a position of perceived absolute superiority to one of deterrence and retaliation.21
• Escalation to Thermonuclear Weapons: In an effort to maintain a strategic edge, the U.S. pursued the development of thermonuclear bombs, which possessed vastly greater destructive potential than the original fission bombs. This triggered a competitive cycle of research and development, with the Soviets following suit shortly thereafter.21
• Strategic Shifts: The realization that nuclear weapons could not be "un-invented" led to the development of complex doctrines like mutual assured destruction, as both superpowers sought to prevent conflict while simultaneously building up their respective arsenals and delivery systems, such as ICBMs.15