Mexico threatened to wage war against the United States if Texas was allowed to join the union. After nine years, Texas was finally admitted as a state. Mexico was furious!

The United States claimed that the river called the Rio Grande was the southern boundary of the United States. Mexico disagreed. American soldiers went to the area to protect US claim, and Mexican soldiers attacked them. The United States declared war on Mexico.

The Mexican War lasted for two years. In 1848, Mexico surrendered. The Treaty of Guadalupe-Hidalgo officially ended the war. The treaty also allowed the United States to buy a 2,000,000 acres of land from Mexico for $15 million. This land, called the Mexican Cession, would become the state of California as well as other southwestern states.

Now the territories of the United States stretched from the Atlantic Ocean to the Pacific Ocean, from sea to shining sea!

The Wilmot Proviso was a bill written by David Wilmot, a Congressman from Pennsylvania. The bill intended to outlaw slavery in newly gained territory from Mexico. Northerners supported it, but Southerners did not. It’s existence led to more division over slavery and was eventually helped lead to the Civil War. The Wilmot Proviso bill never became law.