When Lincoln was president, seven states had seceded from the Union to become the Confederate States of America. They took control of all forts and other government property in these areas, but two they were not able to immediately acquire--Fort Sumter in South Carolina and Fort Pickens in Florida.
John J. Critenden of Kentucky attempted to draw up a compromise know as the Critenden Compromise. Its provisions were that slavery would be permitted in the Confederate States and that the boundaries set forth by the Missouri Compromise would be reestablished (to the north slavery would be prohibited and to the south it would be permitted). The Republicans, however, refused to agree to this compromise because it consented to the existence of slavery.
As the disagreements furthered, the northern soldiers in Fort Sumter became in need of supplies. Lincoln was prohibited by the governor of South Carolina to send supplies, but he did so anyway, and his troops were attacked.
This marked the beginning of the Civil War.
As far as whether or not the Civil War was inevitable, there are historians who argue this topic. First of all, there are arguments over the cause of the war, whether it was because of the issue of slavery or because the North wanted to reunite with the South. According to James Rhodes, "if the Negro hadn't been brought to America, the Civil War would have not occurred," meaning that slavery was the definite cause of the war, and not only for moral reasons but also for economic ones. While it was beneficial to some southerners to own slaves, the northerners did not want this system to trickle into the North.
Other historians argue that the war could have been avoided. Randall felt that it was because of the incompetent...