defense

National defense is the protection of a country's sovereignty and borders from external threats. This involves maintaining military forces to deter potential aggressors and resist attacks. The study of the economic aspects of this, including military expenditure and wartime economics, is known as defense economics.1

A key concept in national defense is deterrence, which aims to prevent war by demonstrating a nation's ability to inflict significant damage on an aggressor, making the costs of conflict outweigh any potential gains. This requires allocating resources for military capabilities, though the exact level of defense spending is a complex question with no simple answer.23

In the United States, the Department of Defense is responsible for national security and supervising military forces, comprising various branches like the Army, Navy, and Air Force. Defense spending includes personnel costs and the procurement of weapon systems, which contribute to a nation's long-term defense capability, considered a "stock" of resources.453