Complex sentence: The earliest recorded date of American Indians becoming U.S. citizens was in 1831 when the Mississippi Choctaw, after the ratification of the Treaty of Dancing Rabbit Creek, were the first non-European ethnic group to become so.
Split into simpler sentences: The earliest recorded date of American Indians becoming U.S. citizens was in 1831. The Mississippi Choctaw after the ratification of the Treaty of Dancing Rabbit Creek were the first non-European ethnic group to become so.