What factor contributed to the United States reducing the size of its military forces after World War II?

The psychological assurance from having the atomic bomb significantly influenced the United States' decision to reduce the size of its military forces after World War II. With the development and possession of nuclear weapons, U.S. military leaders and policymakers believed they had gained a formidable deterrent against potential adversaries. This newfound capability allowed the U.S. to reassess its conventional military needs, as the deterrent effect of nuclear arms provided a level of security that diminished the perceived necessity for large standing forces.

As the doctrine of mutually assured destruction emerged, the emphasis on nuclear deterrence shifted military strategy away from large ground forces and conventional warfare to a focus on strategic capabilities and air power. The confidence in the atomic bomb created a mindset that the U.S. could maintain security and prevent conflicts through the threat of overwhelming retaliation instead of through a vast conventional military presence.

While the emergence of NATO and the geopolitical landscape played roles in military strategy and defense policy, they did not directly drive the reduction of forces in the same way that the psychological assurance provided by nuclear weapons did. The end of the Great Depression is unrelated to military size decisions, as it pertained more to economic recovery and stability rather than military considerations.