Mexican American War- President Polk believed that war with Mexico would bring not only Texas into the Union, but also New Mexico and California. Mexicans killed 11 US soldiers and they declared war. US won and signed the Treaty of Guadalupe Hidalgo.

Right after the United States gained new territory from winning the Mexican American War, a carpenter discovered gold while working near Sutter’s sawmill. Soon after, people from all corners of the country and the rest of the world began to flock to California in search for gold. The population of California skyrocketed from 400 in 1848 to 44000 in 1850. The discovery of gold revolutionized.

The Treaty of Guadalupe Hidalgo (gwah-dah-loop-ay ee-dahl-go), which brought an official end to the Mexican-American War (1846-1848) was signed on February 2, 1848, at Guadalupe Hidalgo, a city north of the capital where the Mexican government had fled with the advance of U.S. forces. To explore the circumstances that led to this war with Mexico, visit the Teaching with Documents lesson, "Lincoln's Spot Resolutions."

https://www.archives.gov/education/lessons/guadalupe-hidalgo/