The United States Civil War (1861–1865) was the bloodiest war in U.S. history. It was fought between the Union (the northern states) and the Confederacy (the southern states). The Confederate states seceded, or left, the United States in 1861. Hundreds of thousands of soldiers were killed during the Civil War. More than 50 major battles were fought. Below are five of the most important.

First Bull Run (July 21, 1861)

The first Battle of Bull Run was the war's first major battle. It is also known as the first Battle of Manassas.

The battle began after Union forces under General Irvin McDonnell marched out of Washington, D.C. Their goal was to seize the Confederate capital of Richmond, Virginia. About 42 kilometers (25 miles) into the march, their path was blocked by the Confederate Army. Confederate forces were commanded by General P.G.T. Beauregard.

Fighting broke out early in the morning. At first, it seemed as if the Union Army would win. However, the Confederates held their ground. More Confederate troops arrived that afternoon. The now-stronger Confederate Army quickly defeated Union forces, who retreated to Washington.

About 4,800 soldiers from both sides died that day.

Shiloh (April 6–7, 1862)

In April 1862, the Union Army set out to seize control of an important Confederate train line in Mississippi. To defend the line, Confederate forces gathered in the town of Corinth, Mississippi. They were under the command of General Albert Sidney Johnston.

The Union planned to unite two armies and then take Corinth. One Union Army unit was under the command of Ulysses S. Grant. The other was led by Don Carlos Buell.

Grant's army arrived first and set up camp in the town of Pittsburg Landing, Tennessee, near the Shiloh Meeting House. Johnston wanted to strike Grant's army before Buell arrived, and at dawn on the sixth of April, his forces attacked. Grant's men were surprised but fought back fiercely. Buell's forces finally arrived overnight, and the combined Union force attacked at dawn. During the fighting, General Johnston was killed. Confederate forces were defeated and pulled back.

More than 23,000 men from both sides were killed during the battle.

Antietam (September 17, 1862)

Confederate General Robert E. Lee had decided to take the war to the North. He came up with a plan to attack Maryland, Pennsylvania, and Washington, D.C. His plan, however, fell into Union hands, and the Union Army marched to meet Lee's forces at Antietam Creek in Maryland. However, Union General McClellan waited 18 hours before moving his troops. This gave the Confederates time to bring in reinforcements.

The long day of fighting ended in a draw, with 23,000 men killed.

Gettysburg (July 1-3, 1863)

After Antietam, Lee gave up his plans to invade the North. However, by the summer of the next year, he was ready to try again.

Lee ordered his forces to march north. They were met by Union troops at the town of Gettysburg, Pennsylvania, on the morning of the first of July. Union forces were under the command of General George Meade.

The Confederates had the upper hand at first, but the Union Army held on and kept them from advancing. The following day, additional troops arrived for both sides. Lee again failed to defeat the Union Army.

On the third of July, the Confederates made one last push. Lee ordered 15,000 Confederate troops to charge up Cemetery Ridge. This attack later became known as Pickett's Charge. Although it broke through Union lines, in the end, the Confederates were pushed back.

Lee's forces retreated on the fourth of July.

The Union side lost 23,000 men, while the Confederates lost 28,000.

Vicksburg (May 22–July 4, 1863)

Vicksburg, Mississippi, is located midway along the very important Mississippi River. Capturing it would give control of the entire Mississippi to the Union. But the city was heavily defended by Confederate forces commanded by General John C. Pemberton.

In May, Union troops under General Ulysses S. Grant attacked Vicksburg and quickly surrounded the city. By mid-June, Confederate soldiers trapped inside Vicksburg were running low on supplies. General Pemberton surrendered on the fourth of July.

The Union victories at Gettysburg and Vicksburg came just a day apart. Together, they marked the turning point of the Civil War. From then on, the North had the upper hand and was victorious.

Many of the battlefields are now national parks and can be visited to learn more about the battles.