In the 1700s Spain feared England and Russia would colonize Alta (upper) California, so they made an effort to establish a permanent settlement first.
In order to protect its interest in North America and to continue the chain of missions started in Baja California, King Carlos III of Spain set up the Sacred Expedition. The idea was to turn the Native Americans into civilized gente de razon (people of reason) and to take advantage of the labor they could provide in building missions and tending the land. The mission period lasted over 50 years. They were set up as self-sustaining mini-cities that could provide food and supplies for everyone who lived in the mission as well as the presidios and nearby pueblos. The padres choosing the mission sites found the best lands for cattle and sheep grazing; growing crops like wheat and vegetables; planting fruit orchards, and vineyards. This valuable land was envied by settlers who did not belong to the Spaniard military and was a major cause for the Mexican Independence Revolution and the Secularization Act.