The event that sparked the American Civil War was the attack on Fort Sumter on April 12, 1861. Tensions between the Northern states and Southern states had been escalating over issues such as slavery, states' rights, and economic differences. When Southern forces fired upon the federal fort in Charleston Harbor, it marked the beginning of armed conflict between the Union and the Confederacy. This incident galvanized public opinion in the North and led to a call for troops, officially starting a war that would reshape the nation and ultimately culminate in the abolition of slavery.