Abraham Lincoln came into office facing a secession crisis. South Carolina, Mississippi, and Florida had seceeded. Mississippi and Florida both rescinded their secession, but South Carolina hadn't.
Fort Sumter Attack
The South Carolina Militia attacked Fort Sumter shortly into Lincoln's term. However, it had been heavily fortified under Cass and the militia lost. Afterwards the South Carolina state government agreed to negotiate an end to the secession.
Compromise of 1861
The Compromise of 1861 strengthened the penalty for violating the Fugitive Slave Law, granted popular sovereignty in all US territories and states on the issue of slavery. This brought South Carolina back into the Union, but disgraced Abraham Lincoln within his own party.
Construction on a transcontinental railroad began.
Radical Republicans lead by Fremont come up with the Amendment Strategy. The idea is to get enough support to amend the Constitution and ban slavery. Needing 3/4s of the states northern states begin entertaining the idea of breaking themselves up to help reach the number. Michigan separates the state of Superior which is recognized in 1862 by Congress. California and Oregon break off land to form the state of Jefferson. Long Island breaks from New York the following year. Washington is made a state just above Oregon in spite of its sparse population. Nevada is also made a state in 1864. The state of Albania, named after Albany is formed in northern New York that same year.
The Utah Territory had been ambiguous about slavery, legalizing it in 1852, although indentured servitude was promoted as being more moral than slavery. With Republicans in power and willing to do what ever they could to get new free states to approve of a constitutional amendment to ban slavery and with tensions over polygamy Brigham Young decided to seize the opportunity and made a bold speech condemning slavery, while still maintaining that blacks were inferior and stating his belief that they would naturally form a lower class even without slavery but that God didn't like slavery due to the poor treatment of slaves. As a result Deseret is seriously considered by the Republican Party as a state to admit to the United States. Although some members oppose it due to the party's history of condemning Mormonism and polygamy. In 1862 it applies for statehood at the time its western border is in OTL Nevada and its eastern borders extend further east than OTL present day Utah. Republicans are divided on whether to accept it. In 1862 Republican representation in Congress grows, and enough of them support statehood for Deseret. Statehood is approved in 1863. Many Democrats use this to morally condemn the Republican Party and accuse them of moral hypocrisy, since they had used polygamy as an attack against Democrats in previous elections. Republican newspapers begin reframing the issue of polygamy portraying it in less harsh terms as simply being a voluntarily entered into contract like monogamy. This would lead slowly to the present day legal status of polygamous marriage in the United States.
The Radical Republicans split with the Republican Party pitting Abraham Lincoln against John C Fremont. This gives the Democratic Party and its candidate Lewis Cass an easy win. Lewis Cass runs emphasizing that he kept the Union together with his decisive action before Lincoln took office.