Lesson 1: War and Territory

Many Americans believed in Manifest Destiny, the idea that the United States was meant to stretch from the Atlantic to the Pacific Ocean. This belief led to war with Mexico. Even before the armies arrived, American settlers in Sonoma started the Bear Flag Revolt.

They captured the town, raised a homemade flag with a grizzly bear, and declared California an independent republic. Although this republic lasted only a few weeks, it signaled the end of Mexican rule. Soon after, the U.S. military arrived and took control.

In 1848, the United States and Mexico signed the Treaty of Guadalupe Hidalgo to end the war. In this agreement, Mexico was forced to give up half its territory to the U.S., including present-day California, Nevada, and Utah.

This treaty officially drew a new border between the two countries. Overnight, California changed from a Mexican territory to a U.S. possession. The treaty promised that Mexican citizens living there would become U.S. citizens and keep their property rights.

Despite the treaty's promises, Californios (Mexican families in California) faced a hard legal battle. The U.S. government passed the Land Act of 1851, which required landowners to prove their land titles in court.

Because the old maps (diseños) were often vague, it was difficult to prove ownership under strict American laws. The legal battles were long and expensive. Many Californio families went bankrupt paying for lawyers and were forced to sell their ranchos, losing their political and economic power.