The U.S. has fought wars ever since its founding – since before its founding, really, since it took a war for us to win our independence from Britain and establish the nation in the first place. But of all those conflicts, the Civil War took the highest toll. 

From 1861 to 1865, the brutal internecine conflict fought on American soil claimed the lives of almost 250,000 combatants on both sides – and the total casualty count was at least 620,000, and according to recent scholarship may have exceeded 800,000. It should be noted that “casualties” includes those killed in battle deaths but also those wounded, captured, or missing in action, as well as those who died away from the battlefield from accident or disease. (These are the states with the most Civil War deaths.)

Battles raged on both Southern and Northern lands, and each inflicted huge losses on both sides. But the 10 detailed here stand out as the most violent.

To determine which battles to include on our list, 24/7 Tempo reviewed statistics on the data site Statista, which in turn drew its statistics from the American Battlefield Trust, an organization that preserves America’s battlegrounds, and the U.S. Department of Defense.

At the cost of 3,654 lives, the Battle of Antietam ranks as the deadliest one-day battle in U.S. history until World War II. But a Union victory on the battlefield in Maryland gave President Abraham Lincoln the political clout he needed to release the Emancipation Proclamation. 

Click here to read about the most violent Civil War battles

With 19,233 casualties and 1,611 deaths, the Siege of Vicksburg gave the North a pivotal victory, as well. When General Ulysses S. Grant took over the port city on the Mississippi, the Union gained control of the river and cut off a vital supply line to the South. 

The true turning point of the war came in the small town of Gettysburg, Pennsylvania. Over three days from July 1 to July 3, 1863, the Union army under George G. Meade and Confederate forces led by Robert E. Lee waged a fierce battle. In the end, the Union prevailed, but a total on both sides of more than 7,000 soldiers (and as many as 5,000 horses) were killed. By stopping Lee’s army from invading the North, the Union crushed the South’s hopes of a victory. Lee would fight other victorious battles, but Gettysburg paved the way for the Union’s eventual victory. (These were the largest battles of the Civil War.)