Why did Americans slaughter Indians? Didn't the Indians help them?

Land, line up. The development of the United States needs a lot of land resources, and they have been robbing the Indian territory. Besides, Americans hate Indians very much. During the War of Independence, Washington hoped that Indians would help the Continental Army, but most Indian tribes chose to help the British, who gave them firearms and other weapons. After the victory of the United States, Washington began to slaughter Indians, burn villages to kill people, and kill bison that Indians could survive.