When the Treaty of Guadalupe Hidalgo was signed in 1848, the US contained fifteen free and fifteen slave states. Controversy surrounded all of the proposed solutions to the problem of slavery in the territories. Additionally, northerners railed against the legality of slavery in the District of Columbia, and southerners, in turn, complained of northern failure to comply with the Fugitive Slave Law. All of these issues had to be resolved if new states were to enter the Union.
