Complex sentence: Allied bands of Lakota, Cheyenne, and Arapaho, under the leadership of Red Cloud, attacked the troops at both Forts Phil Kearny and C.F. Smith.
Split into simpler sentences: Allied bands of Lakota, Cheyenne, and Arapaho were under the leadership of Red Cloud. They attacked the troops at both Forts Phil Kearny and C.F. Smith.