Ace the CSET 1 MCS & CR 2026 – Ignite Your Teaching Journey!

When territories change hands, it reshapes who lives there and under what government. The Treaty of Guadalupe Hidalgo, signed in 1848, ended the Mexican-American War and transferred California and much of the Southwest to the United States. With California now part of the U.S., Mexican residents who were living there came under U.S. law, and many people from Mexico moved into the region as its political status shifted. The treaty also promised to respect existing property rights and offered a pathway to U.S. citizenship for those who stayed, which helped integrate Mexican communities into California under the new sovereignty.

The other events don’t fit this idea: a Mexican Revolution was a conflict, not a treaty that redefined California’s sovereignty; the Gadsden Purchase was a later land purchase mainly for a southern route to the railroad; the California Gold Rush describes a population surge driven by gold, not a diplomatic agreement.