The Defiant Agents (Time Traders Series #3)

The star traveling secrets brought back by time travellers have been unravelled, and both the Americans and the Russians are intent upon colonizing new worlds. A unique method of adapting effete Earthlings to frontier worlds is being used: the colonists are hypnotically regressed to the mentality of their fierce ancestors. Thus, on Topaz, we find a band of Apaches representing the West and a horde of Mongols sent by the East.