Why did spain create missions in the colonies?

To assimilate american-Indians, is the right answer.

Explanation:

The Spanish missions in California include a group of 21 religious missions installed in the years between 1769 and 1833, in the State of California in the United States. These missions were introduced to convert the American-Indians. Following the long-term earthly and religious course of Spain in Spanish America, the evangelists urged the native people to live in towns called reductions, disturbing their traditional way of life.