Lee left the federal army when Virginia said it was leaving the United States. He decided he could not fight against his home state. He became the leader of the armed forces of the Commonwealth of Virginia. He then became commander of the Army of Northern Virginia. Lee was a great commander and won several battles against the Union forces. Most Union officers thought Lee had broken his promises to the Union because he chose to fight against them. Part of Arlington was taken away from the Lee family and became a graveyard. Mostly Union dead are buried there.