The Armed Forces of the USA include the Army, Navy, Air Force, Marine Corps and Coast Guard. The regular components are manned by both men and women who make the military life their profession. Under the Constitution of the United States the President is the Commander-in-Chief of the Armed Forces. The President is assisted by several agencies - the US Security Council and the Central Intelligence Agency (CIA).
The Secretary of the Army, a civilian, is the head of the Army. He is assisted by other civilian officials and by the Army Staff.
Americans go to Army because the salary in the Army is stable and high, the meals for soldiers are free. You may travel all over the world because there are a lot of military bases in many countries. You may get a new profession. The Pentagon pays for your University course. And even when you leave the Army, they will take care of you during the rest of your life (special hospitals and so on). Women join the Army because they want to have equal rights with men.
The Pentagon is the military center of the United States. In April 1949, the USA set up a military organization in Europe called NATO (North Atlantic Treaty Organization). There were 12 countries there.