1835 American settlers in Texas declare their independence from Mexico. Louisiana intevenes because they are afraid that Texas will join the USA if left on their own, which would leave Louisiana utterly encircled. The Mormons settle on the Great Salt Lake and found the semi-autonomous state of Deseret within Mexican territory. 1846 American settlers in Oregon petition for annexation to the US, but the slave states vote the request down. Instead, the Oregonians establish a sovereign government themselves.
Gold is discovered in California.
Immigrants from all over the world pour in. Working in secret alliance, California and Deseret declare their independence from Mexico, while Texas pushes its border from the Nueces to the Rio Grande. Mexico, however, is forced to recognize the new nations. Although the free state voting block had been weakened by the secession of New England, the slave state voting block had not been boosted by the addition of Texas, Louisiana and Florida. The House of Representatives has already shifted to a free state majority, and with the election of Abraham Lincoln of the abolitionist Republican Party to the presidency, the south fears that slavery may soon be abolished altogether.