The Gaspar de Portolá land expedition in 1769 led to the founding of Mission San Gabriel by Christian missionary Junipero Serra in 1771 and initiated an era of forced relocation, enslavement, and exposure to Old World diseases. This led to the rapid collapse of Tongva society and lifeways. Resistance and rebellions occurred in retaliation, including an unsuccessful rebellion in 1785 by Nicolás José and female chief Toypurina. In 1821, Mexico gained its independence from Spain and secularized the missions, selling mission lands to ranchers and forcing the Tongva to assimilate. Most became landless refugees during this time. In 1848, California was ceded to the United States following the Mexican-American War. The US government signed 18 treaties between 1851 and 1852 promising of land for reservations. However, these treaties were never ratified, and were negotiated with people who did not represent the Tongva and had no authority to cede their land. During American occupation, many of the people were targeted with arrest and used as convict laborers in a system of legalized slavery to expand the city of Los Angeles for Anglo-American settlers, who became the new majority in 1880.