Fort Sumter

On April 12, 1861, Fort Sumter in South Carolina was attacked by the Confederacy beginning the Civil War. From the article:

"Fort Sumter
Charleston Harbor, SC | Apr 12 - 14, 1861
The attack on Fort Sumter marked the official beginning of the American Civil War—a war that lasted four years, cost the lives of more than 620,000 Americans, and freed 3.9 million enslaved people from bondage.

How it ended
Confederate victory. With supplies nearly exhausted and his troops outnumbered, Union major Robert Anderson surrendered Fort Sumter to Brig. Gen. P.G.T Beauregard’s Confederate forces. Major Anderson and his men were allowed to strike their colors, fire a 100-gun salute, and board a ship bound for New York, where they were greeted as heroes. Both the North and South immediately called for volunteers to mobilize for war.

In context
By 1861, the country had already experienced decades of short-lived but ultimately failed compromises concerning the expansion of slavery in the United States and its territories. The election of Abraham Lincoln as president of the United States in 1860—a man who declared “I believe this government cannot endure permanently half slave and half free”—threatened the culture and economy of southern slave states and served as a catalyst for secession. On December 20, 1860, South Carolina seceded from the United States, and by February 2, 1861, six more states followed suit. Southern delegates met on February 4, 1861, in Montgomery, AL., and established the Confederate States of America, with Mississippi senator Jefferson Davis elected as its provisional president. Confederate militia forces began seizing United States forts and property throughout the south. With a lame-duck president in office, and a controversial president-elect poised to succeed him, the crisis approached a boiling point and exploded at Fort Sumter."