How does the Treaty of Guadalupe Hidalgo possibly cause issues for Southern Slave owners and Northern States who dislike slavery?

The Treaty of Guadalupe Hidalgo, signed on February 2, 1848, ended the Mexican-American War in favor of the United States. The war had begun almost two years earlier, in May 1846, over a territorial dispute involving Texas. The treaty added an additional 525,000 square miles to United States territory, including the including the land that makes up all or parts of present-day Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming. Mexico also gave up all claims to Texas and recognized the Rio Grande as America's southern boundary.

Mexican-American War: 1846-48

On May 13, 1846, the U. S. Congress voted in favor of President James Polk's request to declare war on Mexico in a dispute over Texas. Under the threat of war, theUnited States had refrained from annexing Texas after the latter won independence from Mexico in 1836. But in 1844, President John Tyler (1790-1862) restarted negotiations with the Republic of Texas, culminating with a treaty of annexation.

Did you know? During his presidency, James Polk managed another important land acquisition, this time without a war, when his administration diplomatically settled a border dispute with the British and gained control of the present-day states of Washington, Oregon and Idaho, plus parts of Montana and Wyoming.

The treaty was defeated by a wide margin in the U. S. Senate because it would upset the slave state-free state balance between North and South and risked war with Mexico, which had broken off relations with the United States. But shortly before leaving office and with the support of President-elect Polk (1795-1849), Tyler managed to get a congressional resolution passed and then, on March 1, 1845, signed into law. Texas was admitted to the union on December 29 of that year.