The Â“Mexican CessionÂ" refers to lands surrendered, or ceded, to the United States by Mexico at the end of the Mexican War. The terms of this transfer were spelled out in the Treaty of Guadalupe Hidalgo of 1848.
To the United States, this massive land grab was significant because the question of extending slavery into newly acquired territories had become the leading national political issue.
To Mexico, the loss of an enormous part of its territory was a tremendous embarrassment and created lasting anger among many of its citizens.
Under the terms of the cession, the United States acquired the territory that became the states of California, Nevada, Utah, and Arizona, with the exception of that territory that later was added by the Gadsden Treaty in 1853. The price of this was $15 million to Mexico and $3,250,000 to cover the claims of American citizens against Mexico.