Early in 1848, Mexico and the US signed the treaty of Guadalupe Hidalgo.

U.S.

Mexico

 Mexico agreed to offer up Texas and a huge region referred to as the Mexican Cession. (Included what is now present day California, Nevada, Utah, Arizona, New Mexico, and parts of Colorado and Wyoming.)

Under this agreement, Mexico gave up half its territory.  

okay here you go

In exchange the US then agreed to pay Mexico $15 million. It also promised to guard the 80,000 to 100,000 Mexicans living in Texas and within the Mexican Cession. Most of these promises were not kept.

Some senators spoke up to oppose the treaty.

NOOOOOOO! We DON'T agree!!!!!

They argued that the US had no right to any Mexican territory other than Texas. They thought the Mexican-American War had been unjust, and the treaty was even more unjust. They thought New Mexico and California together were not worth a dollar and should be returned to Mexico. 

We only should get Texas.

Some other senators opposed the treaty because they wanted even more land. They wanted the Mexican Cession to include a large part of northern Mexico as well.  

Give us even more land we want it.

To most senators the Mexican Cession was a manifest destiny dream come true. The Senate ratified the treaty by a vote of 38 to 14.

In 1853 the U.S. acquired more land.