The Tepehuán suffered a series of devastating epidemics of European-introduced diseases in the years before the revolt. Epidemics were known to have occurred in their region in 1594, 1601-1602, 1606-1607, 1610, and 1616-1617.  The Tepehuán and their neighbors may have been reduced in population by more than 80 percent by the epidemics, from a pre-Columbian population of more than 100,000 to fewer than 20,000,  of which the Tepehuán may have been one-half of this total During the Chichimeca war  the Tepehuán remained neutral although urged by the Chichimecas to join them in resistance to Spanish expansion. The Spanish failed to defeat the Chichimeca militarily and instituted a new policy called "peace by purchase" in which Catholic missionaries would be a major tool in pacifying hostile and semi-hostile Indians.  Indians were to be supplied with food and tools and resettled into towns. Missionaries, rather than the military, would take on most of the responsibility for integrating the Indians into Mexican and Christian society.  The Acaxee and Xixime were the first to have this new Spanish policy applied to them and the Tepehuán would be next.. How many years was there in between the first year where epidemics were known to have occurred and the last year?