The United States Army is the major ground-based defensive force of the United States as of 1792.
United States Army . As the largest and senior branch of the U.S. military , the modern U.S. Army has its roots in the Continental Army , which was formed ( 14 June 1775 ) to fight the American Revolutionary War ( 1775 -- 1783 ) -- before the U.S. was established as a country .