Complex sentence: He denounced Americans as children of the Evil Spirit and mobilized the Indians in the Midwest to fight them, but his movement was defeated in the War of 1812 when his brother was killed, and he went to the area now known as Argentine, Kansas.
Split into simpler sentences: He denounced Americans as children of the Evil Spirit and mobilized the Indians in the Midwest to fight them. But his movement was defeated during the War of 1812 when his brother was killed, and he went to the area now known as Argentine, Kansas.