Boom! A single cannon shell burst in a flash of light high above Fort Sumter. This was the signal for the Confederate attack on the U.S. fort to begin. It was also the moment our Civil War began — 4:30 a.m. on April 12, 1861 — 150 years ago this week.

For 34 hours, Confederate cannon fire from the shores of South Carolina’s Charleston Harbor battered the towering walls of the island fortress as fiery shells crashed into the open area in its center. The noise was deafening, and thick smoke made it hard for the defenders of the U.S. fort to see — or breathe. With little ammunition, they fired back just often enough to let the Southerners know they were still fighting.

Who were Sumter’s defenders? Just 82 soldiers — including members of the military band — aided by about 40 workmen employed at the fort. The soldiers knew it was their duty to defend U.S. property that President Abraham Lincoln had vowed to protect. But they were greatly outnumbered.

Finally, with fires raging inside, Fort Sumter’s commander surrendered. A great shout went up from the Confederates when they saw a white flag of truce replace the battle-torn American flag that had flown over the fort.

For months, that flag had angered the Southerners. They didn’t want a U.S. fort in Southern territory, but Lincoln, who had taken office the month before, had made it clear he wouldn’t give it up. When he told South Carolina’s governor that he was sending an unarmed supply ship to the men inside Sumter, it was the last straw. Confederate leaders decided to bombard the fort unless the U.S. soldiers left right away. But their orders were to defend the fort, so they did.

The bombardment of Fort Sumter was the first battle of the American Civil War. Force had finally brought an end to the standoff between North and South. Here’s what happened next:

In the South, Confederates rejoiced at their victory. People cheered and rang church bells.

A wave of patriotism swept through the North. Enraged that the U.S. flag had been fired on, people organized parades and public meeting to show support for their government. Lincoln called for volunteers to serve for 90 days and put down the rebellion of the seven deep-South states that had formed the Confederacy. He also called for a blockade of Confederate ports so the South couldn’t import goods — including weapons — or export their cotton and tobacco.

Virginia seceded from the United States and joined the Confederacy rather than send volunteers to fight against “her sister states.” Three other Southern slave states quickly moved toward secession. Soon, the Confederacy would include 11 states, and the Union would include 23.

The first blood shed during the war is widely accepted to have been in Maryland. A riot broke out in Baltimore when U.S. volunteers answering the president’s call passed through on their way to Washington — increasing Lincoln’s concern that Maryland, too, might secede.

All this happened during the first week after Fort Sumter. In coming weeks, young men rushed to sign up to fight. Both North and South were sure they would win — and win in a matter of months. But they were wrong. The bombardment of Fort Sumter began four long, hard years of war.

— Carolyn Reeder

Reeder is an award-winning children’s author who is writing a series of stories for KidsPost giving readers a kids’-eye view of the Civil War. She is the author of “Shades of Gray” and “Captain Kate.”