What were the circumstances in Fort Sumter that allowed it to be the birth place of the Civil War?
It was a Federal Fort in South Carolina.
South Carolina seceded from the Union in late December 1860, shortly after Lincoln's election. Other states seceded and the Confederacy was formed in February 1861.
Fort Sumter sits just outside of Charleston in the harbor. The strategic location of this fort and it being in federal hands did not sit well with South Carolinians. When President Lincoln announced plans to resupply the fort, Confederate Gen. Beauregard bombarded the fort on April 12, 1861. The next day it was in Confederate hands.