The U.S. Army is responsible for securing America's geographical borders and the citizens who reside in it by military means. Additionally, the Army provides military support when needed by local authorities in crisis and formulates defense strategies for military operations.
To provide necessary forces the expertise to carry out their missions, national defense being just one, the U.S. Army trains and equips soldiers to engage in combat and stability operations on land. The War on Terror, which began shortly after the 9/11 attacks, is another commitment in which the Army takes part in combating. The U.S. Army also partakes in multinational exercises to solidify and maintain treaties with other alliances and organizations.
The Army also helps defend allies, including South Korea, Japan and many other nations. While on a perpetual mission to secure the national borders of the United States, the Army takes part in an effort to curtail illegal drug trafficking as well.
The U.S. Army is the oldest branch of the U.S. defense forces and is the largest as of 2015. The Second Continental Congress founded the U.S. Army in 1775, originally to defend the 13 colonies, then still under British rule. The Army has since grown into one of the world's most formidable fighting forces.