Hood's education at the United States Military Academy led to a career as a junior officer in both the infantry and cavalry of the antebellum U.S. Army in California and Texas. At the start of the Civil War, he offered his services to his adopted state of Texas. He achieved his reputation for aggressive leadership as a brigade commander in the army of Robert E. Lee during the Seven Days Battles in 1862, after which he was promoted to division command. He led a division under James Longstreet in the campaigns of 1862–63. At the Battle of Gettysburg, he was severely wounded, rendering his left arm useless for the rest of his life. Transferred with many of Longstreet's troops to the Western Theater, Hood led a massive assault into a gap in the Union line at the Battle of Chickamauga, but was wounded again, requiring the amputation of his right leg.