Territorial Expansion and Effects

Event Notes

Wilmot Proviso


Whig Congressman David Wilmot propses a law that would ban slavery in any lands won from Mexico. The law passes in the House, but narrowly fails in the senate. The law also broke party unity, Southern Whigs sided with Southern Democrats and Northern Whigs sided with Northern Democrats. The lands won from Mexico increase tensions between South and North.


1847 - 1852

People come from Peru, Chile, and China to strike it rich in California. The population soars from 14,000 in 1847 to 225,000 in just five years.

John Sutter

January, 1848 - March, 1848

John Sutter's sawmill finds gold specks in the American River east of Sacramento, California. This event sets off the California Gold Rush in which 80,000 fortune seekers head for California to try and strike it rich.

Treaty of Guadalupe Hidalgo

February, 1848

A Treaty between the Mexicans and Americans that forces Mexico to give up the northern third of their country and adds 1.2 million square miles of territory to the US. The treaty disgusts and humiliates Mexicans who continue to feel bitterness towards the US for decades. Polk is unhappy because he did not win enough land in his eyes, but settles for the treaty as northern public opinion would not support a longer war.

California's Statehood

October, 1849

Leaders hold a convention to draw up a state constitution of California. This constitution excludes all African Americans. The Californians, mainly northerners, did not want to compete with slave labor or have free blacks live there.
California's application for statehood would tip the balance of free and slave states . In the next decade, the issue of slavery in lands won from Mexico would grow increasingly bitter. Westward expansion would be a major factor in the starting of the Civil War.

Gasden Purchase


The US obtains another 29,640 square miles in Southern Arizona and New Mexico from Mexico in this purchase. This strip of land facilitates a railroad across the continent. The new lands from the annexation of Texas, the Treaty of Guadalupe Hidalgo, and the Gasden Purchase increase the size of the US by one third.