Final answer:
The Treaty of Guadalupe Hidalgo ceded California to the United States in 1848.
Explanation:
California changed hands when Mexico and the United States last fought. This land, along with other territories, was ceded to the United States as part of the Treaty of Guadalupe Hidalgo that ended the Mexican-American War in 1848. The United States gained significant land from Mexico through this treaty, expanding its territorial holdings.
Learn more about Mexican-American War and the Treaty of Guadalupe Hidalgo here:
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