Answer based on context:

The Spanish policy evolved to make peace with the Chichimecas had four components: negotiation of peace agreements, welcoming conversion, instead of forcing conversion to Catholicism with missionaries, encouraging native allies to settle the frontier to serve as examples and role models, and providing food, other commodities, and tools to potentially hostile natives.  This established the pattern of Spanish policy for assimilating natives on their northern frontier.  The principal components of the policy of purchase for peace would continue for nearly three centuries and would not be as successful, as later threats from hostile natives such as Apaches and Comanches would demonstrate and as Spaniards would still value any means to riches and break treaties with natives. After the Chichimeca War, the Purchase for Peace Program gradually corrupted. Many Spanish Loyalist resented the defeat. The Spanish loyalist attempted enslavement for mining and agricultural labor, enforced harsh working conditions to the lower social classes, and implemented extremely oppressive political and economic systems against the native and mestizo populations of Mexico. The Catholic Church sustained the Mexican Inquisition torturing and killing hundreds of people who did not convert to Catholicism. The Mexican Inquisition was first abolished by decree in 1812. However, political tensions and chaos led to something of its return between 1813 and 1820. It was abolished in 1820. This societal tension during this period contributed to the initiation of the Mexican War of Independence; which started in 1810 and ended in 1821.

how many policy purchase centuries?
3