The United States Army, more popularly referred to simply as the Army or the US Army, was a branch of the military of the United States of America on Earth. The largest branch of the various armed services of the United States, the Army was responsible for land based military operations. The Army was formed on June 14, 1775 as the Continental Army, and would later play a major role in securing the independence of the United States. George Washington was the leader of the Army at this time.
During the Civil War era, the Army was known as the Union Army. Colonel Thaddius Riker - a distant ancestor of Captain William T. Riker - served in the Union Army during the Civil War. His life was saved when a member of the Q continuum who would come to be called Quinn carried him to safety following the Battle of Pine Mountain, Georgia. (VOY episode: "Death Wish")
As aircraft were developed in the early 20th century, the Army initially took responsibility for aerospace matters. The particular part of the Army responsible for aerospace operations was known as the Army Air Corps. In 1947 that part of the Army was taken to form a separate armed service, known as the United States Air Force.
During the refuge era, almost every species was accepted in the army. For some species, their are certain requirements. For example, Jem'Hadar who want to join the mkilitary must either have an endless supply of White given to them every year or must have the same mutation as Goran'Agar.