Although Jackson served for a brief time in the Revolutionary Army when he was thirteen, his first real military service came as major general of the Tennessee Volunteers from 1813 to 1814. He led a campaign against the Creek Indians who had attacked American settlers north of Mobile, Alabama. He defeated the Creeks decisively at the Battle of Horseshoe Bend in March 1814. On August 9, 1814, Jackson signed the Treaty of Fort Jackson, officially ending the Creek War and causing the Indians to surrender their lands in Georgia and Alabama.

Battle of New Orleans

In 1814, Jackson became a major general in the regular army to fight in the War of 1812. His huge victory came on January 8, 1815, when he defeated the British at the Battle of New Orleans. Ironically, unbeknownst to Jackson or the British, his victory came after the Treaty of Ghent had been signed, officially ending the war. Nonetheless, this battle was a huge popularity boost for Jackson, who became a national hero.

Jackson Disobeys Orders

Jackson left military service until he was recalled to fight in the First Seminole War in December 1817. Seminole Indians and runaway slaves were attacking Georgia from Spanish-held Florida. He was ordered to repel the attackers but instead invaded Spanish Florida — without President James Monroe's authorization.

Jackson's invasion initially caused international censure of the United States and many claimed that Jackson should be disciplined. However, Secretary of State John Quincy Adams was able to spin this so that the United States could blame it on Spanish negligence in protecting their borders. Adams actually used this affair to get the Adams-Onis Treaty signed whereby Spain ceded Florida to the United States.