Ahh...I forgot to explain. Basically, the Southerners began to embark on a campaign of territorial expansion, because they could handle it. They didn't really conquer Mexico as much as kill or displace everyone and settle whites in the area. Later on, a league of Latin American nations will be organized to deal with the Confederate menace.
TL: 1864: Confederacy gets independence, invades and annexes Northern Mexico. US begins industrial boom.
1865: US purchases Alaska and western Canada. Oklahoma granted independence as the Lakota Republic; occupies Oklahoma and a good part of the border around Oklahoma. Many natives move there. Vancouver leased to British for 99 years.
1866: Dominion of Canada granted independence. Quebec splits off, Canada balkanizes rapidly. New nations are Dominion of Canada, Maritime Confederation, Republic of Quebec, Dominion of Newfoundland.
1867: Latin American league formed to counter Confederates. Confederates begin Confederate Pacific railroad to link Richmond with San Luis Potosi. Confederate advance into Mexico halted at Battle of Mexico City. Latin American League includes Central America, most of South America, and Mexico. Those South American nations who aren't members are allies.
1868: Union Pacific railroad completed. Columbian Pacific, linking Union Pacific to Alaska, sometime in future, begun. Slave population in South begins explosion.
1869: Soil exhaustion becomes a problem in some regions of the South. George Washington Carver never comes along to help out using things like soybeans and peanuts to rejuvinate soil, so the problem gets worse. Peanut butter is also never invented. (= I hate that damned accursed stuff.
1870: Black population, including infants, numbers 60% of Southern population. Series of vicious hurricanes hit Florida and Cuba. A surprise storm destroys a Confederate invasion fleet attempting to invade Cuba. Confederacy is defeated once more at the Second Battle of Mexico City.
1871: Latin American league and Confederacy begin bloody war. Confederacy manages to gain control of rest of Mexico, but at a terrible cost. Economy takes downturn, inflation gets even worse. News of horrible Confederate abuses in Mexico reach Europe; everyone gets PO'd at the rednecks. Union begins sending aid to Latins.
1872: Confederacy has nasty year. Erosion becomes serious problem. Violence erupts in the large ghettos erected in cities for black slaves used in factories. Slave population now numbers 75% of the total Confederate population.
1873: Southerners, feeling very nervous, abolish slaves and enact strict apartheid instead. They even plan to grant regions of heavy black settlement independence, o_0. Union buys most of Northwest Territory for twenty million, Greenland for ten million. Washington and British Columbia, which has grown to include the Yukon Territory, is admitted to the Union as a state.
1874: Confederates have extended their borders to Nicaragua. Defeated at battle of Lake Nicaragua, though. San Luis Potosi admitted as a state.
1875: At this point, Miami is a stinking hellhole. It is filled with angry African Americans, who riot regularly. On one particularly nasty riot, the whole city is burned to the ground and over five hundred thousand are killed. The revolt spreads quickly. By the time the army has restored order, most of the African American population is dead, as is most of the Caucasian population. The southern economy takes a downturn, and Florida, incensed at the lack of protection provided by the Confederate military and such, secedes. Because secession is the principle the CSA is built on, there is nothing the CSA can do about it. Before long, the CSA has completely dissolved. The only remainer is Texas, busily conquering itself a Latin American empire.
1876: The Union, seeing the current turmoil as a golden opportunity, begins the Reintegration War. Texas has promised aid to its neighbors in case of an emergency, so Union troops conduct a repeat of the Franco-Prussian war, with the Texans playing the role of the proud, but nonetheless vanquished Gallic warriors. The southern states are reconsolidated by July the fourth, and Texas loses a good deal of its territory to the Union. The Texan front in Panama collapses, and the Latins regain their lost territory. Although the Civil War was won in the short term by the South, in the end, it was the South that lost.