The Civil War began in 1861 when the states in the South (called the Confederacy) declared their independence from the states in the North (called the Union).
Although Indians were not then citizens of the United States, the Confederacy pressured the Five Civilized Tribes to become its allies. Because they had originally lived in the South, they had closer ties to the Confederacy than to the Union.
Not all Indians in Indian Territory, however, wanted to join the Confederacy. Some Indians fought with the Union forces. Many who did had first joined the Confederate army, but decided to switch sides when they grew disillusioned with the Confederacy. Others wanted to fight for the Union only after they were attacked by Confederate troops.
Fighting on both sides, Indians were often pitted against Indians as the war ripped through Indian Territory. The experience was so devastating that, a month after the war ended with a Union victory, 14 tribes signed a declaration, agreeing that they would no longer shed each others’ blood.