Your book implies on page 465 that the Five Civilized Tribes actively supported the Confederacy. Here are some important facts:
Soldiers from the tribes fought on both union and Confederate sides.
Stand Watie, a Cherokee, owned over 100 slaves, and fought on the side of the South as a general. In fact he was one of the last Confederate generals to surrender after Lee’s surrender at Appomattox. He was installed as Cherokee chief after the then- chief, John Ross, was captured by the Union.
John Ross, chief of the Cherokees since before removal from the East, attempted to keep the tribe neutral, but after Confederate general and diplomat Albert Pike came to Indians territory, with a threat of an invasion by Confederate forces from Arkansas and civil war within the Cherokee nation by those affiliated with Stand Watie, Ross reluctantly signed a treaty with the Confederacy. However, a federal force invaded Indian territory in the summer of 1862, and Ross was captured and paroled to Philadelphia, where he pointed out that many Cherokee had fled to Kansas as refugees rather than affiliate with the pro-Confederate faction.
The Creek Indians also split during the Civil War, with a faction signing a treaty with the Confederacy while those who did not wish to do so fled north toward Kansas in the dead of winter, pursued by the fellow tribesmen. The refugee Creek maintained that they were loyal. Most Creek Indians attempted to maintain loyalty to the Union.
The Seminole Nation also maintained loyalty to the Union.
The Choctaw and Chickasaw from southern Indian territory were predominately pro-Confederate.
For the story of the Sioux uprising in Minnesota in 1862, go here: http://www.historycentral.com/CivilWar/people/Native.html
For more information, see Laurence M. Hauptman, Between Two Fires: American Indians in the Civil War (1995)
The Plains Indians
For more info see: http://thomaslegion.net/fivecivilizedtribesandtheamericancivilwar.html