WordNet sense 1 (North American republic containing 50 states - 48 conterminous states in North America plus Alaska in northwest North America and the Hawaiian Islands in the Pacific Ocean; achieved independence in 1776):

us, America, U.S., U.S.A., United States, the States, United States of America

WordNet sense 2 (the army of the United States of America; the agency that organizes and trains soldiers for land warfare):

army, United States Army, U. S. Army, US Army