About 200 years ago, parts of California, Nevada, Utah, New Mexico, and a bunch of other American states belonged to Mexico.
This is called the Mexican Cession.
Most people don’t even know this big piece of land once belonged to Mexico — one of the biggest land transfers in modern history.
In this article, I’ll tell you everything about it.
The Mexican-American War
One major historical event tied to the Mexican Cession is the Mexican-American war that started in 1846.
To understand why this war even started we’d have to go back to Texas in 1836 — the year that they gained their independence.

During the Texas Revolution, Texas was part of Mexico housing a lot of Anglo-American citizens and wanted to become an independent Republic.
This group and the Mexican government of President Antonio Lopez de Santa Anna didn’t get along so well and that caused a revolt to start in 1835 named the Texas Revolution.
They eventually gained their independent state status a year later.
The Republic of Texas remained an independent nation for nearly a decade before being annexed by the United States in 1845, which contributed to the start of the Mexican-American War.
Texas wanted to become part of the United States. Mexico didn’t like that.
The U.S. claimed that the border was the Rio Grande, while Mexico maintained that it was the Nueces River further north. At first, the United States, led by President Polk in 1846 tried to buy the land but those attempts failed.
But what does a US President do when he doesn’t get what he wants? Correct, he just annexes a piece of land and says it belongs to him.
That escalated the situation and the war started.

The End of the War & The Treaty of Guadalupe Hidalgo
The Mexican Cession is a region in the modern-day southwestern United States that Mexico originally controlled and then ceded to the United States.
Following the Treaty of Guadalupe Hidalgo in 1848, which concluded the Mexican-American War.
The Treaty of Guadalupe Hidalgo, signed on February 2, 1848, marked the end of the Mexican-American War.
Apart from ceding over 500,000 square miles of territory to the United States, the treaty also provided certain guarantees.
For instance, Mexican citizens living in the ceded territories were given the choice of returning to Mexico or remaining and becoming full U.S. citizens. Many chose to stay and maintain their cultural heritage.
The Mexican Cession had far-reaching social, economic, and cultural impacts. The newly acquired territories saw a rush of settlers from the eastern U.S., altering the demographics and lifestyle of the region.
Moreover, the discovery of gold in California in 1848 sparked the famous Gold Rush, leading to the state’s rapid economic development.
This territory consisted of present-day U.S. states including California, Nevada, Utah, most of Arizona, the western half of New Mexico, the western quarter of Colorado, and the southwest corner of Wyoming.
The Mexican-American War led to the seizure of territories like Alta California and Santa Fe de Nuevo México, with the U.S. invading central Mexico and occupying Mexico City.
However, no Mexican government was willing to ratify the transfer of these territories.
Eventually, the Treaty of Guadalupe Hidalgo was forged, redefining the border between Mexico and the United States and acknowledging Mexico’s loss of Texas.

The United States paid $15 million.