The first removal treaty carried out under the Indian Removal Act was the 1830 Treaty of Dancing Rabbit Creek, by which the Choctaw people were forced to cede 15 million acres of their homelands to the United States and to move to Indian Territory (now part of Oklahoma), west of the Mississippi River. A similar forced removal of the Chickasaw Nation began in 1837; when they reached Indian Territory, the federal government assigned them to what had been the westernmost part of the Choctaw Nation.