The Mexican Cession was the name given to the land, not including Texas, ceded to the United States by Mexico in the Treaty of Guadalupe Hidalgo. This treaty officially ended the Mexican-American War.
Begun as a dispute over the southern border of Texas, the Mexican-American War eventually led to much larger territorial gains for the United States. The Mexican Cession included all or part of the states of Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming. At around 525,000 square miles, this territory constitutes around 5 percent of the land area of the entire United States. In return for this land and the disputed lands in Texas, the United States paid Mexico $15 million and assumed $3.25 million in debts owed to U.S. citizens.