As of 2017, the U.S. spends about US$610 billion annually to fund its military forces and Overseas Contingency Operations. Put together, the U.S. constitutes roughly 40 percent of the world's military expenditures. The U.S. Armed Forces has significant capabilities in both defense and power projection due to its large budget, resulting in advanced and powerful technologies which enables a widespread deployment of the force around the world, including around 800 military bases outside the United States. The U.S. Air Force is the world's largest air force, the U.S. Navy is the world's largest navy by tonnage, and the U.S. Navy and the U.S. Marine Corps combined are the world's second largest air arm. In terms of size, the U.S. Coast Guard is the world's 12th largest naval force. 
Military history has a number of facets. One main facet is to learn from past accomplishments and mistakes, so as to more effectively wage war in the future. Another is to create a sense of military tradition, which is used to create cohesive military forces. Still, another may be to learn to prevent wars more effectively. Human knowledge about the military is largely based on both recorded and oral history of military conflicts (war), their participating armies and navies and, more recently, air forces.
Prospective service members are often recruited from high school or college, the target age ranges being 18–35 in the Army, 18–28 in the Marine Corps, 18–34 in the Navy, 18–39 in the Air Force and 18–27 (up to age 32 if qualified for attending guaranteed "A" school) in the Coast Guard. With the permission of a parent or guardian, applicants can enlist at age 17 and participate in the Delayed Entry Program (DEP), in which the applicant is given the opportunity to participate in locally sponsored military activities, which can range from sports to competitions led by recruiters or other military liaisons (each recruiting station's DEP varies).
The President, Secretary of Defense and other senior executive officials are advised by a seven-member Joint Chiefs of Staff, which is headed by the Chairman of the Joint Chiefs of Staff, the highest-ranking officer in the United States military and the Vice Chairman of the Joint Chiefs of Staff. The rest of the body is composed of the heads of each of the DoD's service branches (the Chief of Staff of the Army, the Chief of Naval Operations, the Commandant of the Marine Corps and the Chief of Staff of the Air Force) as well as the Chief of the National Guard Bureau. Although commanding one of the five military branches, the Commandant of the Coast Guard is not a member of the Joint Chiefs of Staff. Despite being composed of the highest-ranking officers in each of the respective branches, the Joint Chiefs of Staff does not possess operational command authority. Rather, the Goldwater-Nichols Act charges them only with advisory power.
After World War II, with the onset of the Cold War, the constant technological development of new weapons was institutionalised, as participants engaged in a constant 'arms race' in capability development. This constant state of weapons development continues into the present, and remains a constant drain on national resources, which some[who?] blame on the military-industrial complex.
In the 2000s, women can serve on U.S. combat ships, including in command roles. They are permitted to serve on submarines. Women can fly military aircraft and make up 2% of all pilots in the U.S. Military. In 2003, Major Kim Campbell was awarded the Distinguished Flying Cross for landing her combat damaged A-10 Thunderbolt II with no hydraulic control and only one functional engine after being struck by hostile fire over Baghdad.
The next requirement comes as a fairly basic need for the military to identify possible threats it may be called upon to face. For this purpose, some of the commanding forces and other military, as well as often civilian personnel participate in identification of these threats. This is at once an organisation, a system and a process collectively called military intelligence (MI).