The armed forces of the United States are referred to collectively as the United States Armed Forces (USAF). There are six different branches that make up the United States Armed Forces. These branches include the Army, the Marine Corps, the Navy, the Air Force, and the Space Force. Both the Department of Defense (DoD) and the Department of Homeland Security (DHS), both of which are federal executive departments, act as the principal organs by which military policy is carried out. The President of the United States is the Commander-in-Chief of the Armed Forces, and he or she is also responsible for formulating military policy. The United States has a total of eight uniformed services, which includes all six of its military forces.
The United States Armed Forces have been pivotal in the development of the United States throughout its entire history, beginning with its founding during the American Revolutionary War. The successes that they achieved in both the First Barbary War and the Second Barbary War contributed to the formation of a feeling of national unity and identity. During the American Civil War, they were instrumental in preventing the Confederacy from breaking away from the republic and helping to maintain the integrity of the union. The structure for the current armed forces of the United States was established in 1947 by the passage of the National Security Act, which came into effect after World War II. In addition to establishing the United States Air Force and the National Security Council, the Act also established the National Military Establishment, which is now overseen by the Secretary of Defense. In 1949, it was changed such that the National Military Establishment became known as the Department of Defense. At the same time, the cabinet-level Departments of the Army, Navy, and Air Force were consolidated into the Department of Defense as well.
In terms of the number of people who serve in it, the United States Armed Forces are among the biggest military forces in the world. Their workforce is comprised almost entirely of unpaid professionals who give their time. Conscription into the military has not been practised in the United States since 1973, despite the fact that it was formerly a common practise. The Selective Service System is authorised to continue its practise of male conscription and continues to mandate that all male citizens and residents living in the United States who are between the ages of 18 and 25 sign up for the service.
The United States Armed Forces are often regarded as the most powerful force in the world. In 2019, the United States has the greatest military budget in the world at a total of $693.3 billion US dollars. In 2018, this was equivalent to 36 percent of the total amount spent on military in the globe. Due to the size of its budget, the United States Armed Forces possesses significant capabilities in both defence and power projection. This has led to the development of cutting-edge and highly effective technologies, which in turn enables a widespread deployment of the force across the globe, with approximately 800 military bases located in countries other than the United States. The United States Air Force is the biggest air force in the world, while the Army Aviation Branch of the United States Army is the second largest. The United States Marine Corps Aviation is the world's seventh biggest air arm, while the United States Naval Air Forces are the world's largest naval aviation service and the fourth largest air force in the world respectively. According to tonnage, the United States Navy is the biggest navy in the world. The United States Coast Guard is the twelfth biggest maritime force in the world. The United States Air Force Space Force is the only autonomous, operating space force in the world.