The next year, 1797, he served in the U.S. Senate. In April 1798, he resigned his seat in the senate, and was appointed judge in the Supreme Court of Tennessee. He retained this office for six years. In 1805 he fought a duel with Charles Dickinson. Dickinson was killed, and Jackson received a wound from the effects of which he never recovered.
As tensions grew around the impending war in 1812, Jackson joined the army as a Major General. Since 1801 he had been commander-in-chief of the Tennessee militia, but there had been no occasion for him to take the field. Late in 1812, after the disasters in the northwest, the government feared that the British might make an attempt upon New Orleans, and Jackson was ordered down to Natchez at the head of 2,000 men. When war was declared, Jackson set out, and while traveling to Natchez, crushed the Creek Indians at Horseshoe Bend, Alabama. His highlight or the war was when he clamed victory over the British with his army, consisting chiefly of backwoodsmen. The British suffered more than 2,000 casualties while the American sustained six killed and 10 wounded. This win helped to restore the nation's pride following the embarrassing White House torching. Jackson emerged from the war a national hero. While marching back to Tennessee, his soldiers experienced his toughness and dubbed him "Old Hickory.".
At the Battle of Horseshoe Bend, Jackson's Tennessee and Kentucky militia killed over 800 Creek indians, shooting them down in a sheer massacre. More Native Americans died in this battle than in any other in the nation's history. After the battle, Jackson marched on to a dozen defenseless Indian villages, killing women and children and burning everything in his path. Totally defeated, the remaining Creek Indians were then forced by Jackson to give 23 million acres of their land to the United States. .
In 1818 he briefly invaded Spanish Florida to quell Seminoles and outlaws who harassed frontier settlements.