Confederate forces were defeated by the Union Army on the last day of the Battle of Gettysburg (pictured), a turning point in the American Civil War.

The Confederate States Army (CSA), also called the Confederate army or the Southern army, was the military land force of the Confederate States of America during the American Civil War (1861–1865), fighting against the United States forces to support the rebellion of the Southern states and uphold and expand the institution of slavery. On February 28, 1861, the Provisional Confederate Congress established a provisional volunteer army and gave control over military operations and authority for mustering state forces and volunteers to the newly chosen Confederate States president, Jefferson Davis (1808–1889). Davis was a graduate of the United States Military Academy, on the Hudson River at West Point, New York, and colonel of a volunteer regiment during the Mexican–American War (1846–1848). He had also been a United States senator from Mississippi and served as U.S. Secretary of War under 14th president Franklin Pierce. On March 1, 1861, on behalf of the new Confederate States government, Davis assumed control of the military situation at Charleston Harbor in Charleston, South Carolina, where South Carolina state militia had besieged the longtime Federal Fort Sumter in Charleston harbor, held by a small U.S. Army garrison under the command of Major Robert Anderson (1805–1871). By March 1861, the Provisional Congress of the Confederate States meeting in the temporary capital of Montgomery, Alabama, expanded the provisional military forces and established a more permanent regular Confederate States Army.

During the American Civil War, the United States Army, the land force that fought to preserve the collective Union of the states, was often referred to as the Union army, the federal army, or the northern army. It proved essential to the restoration and preservation of the United States as a working, viable republic.

The Battle of Gettysburg was a three-day battle in the American Civil War, which was fought between the Union and Confederate armies between July 1 and July 3, 1863, in and around Gettysburg, Pennsylvania. The battle, won by the Union, is widely considered the Civil War's turning point, leading to an ultimate victory of the Union and the preservation of the nation. The Battle of Gettysburg was the bloodiest battle of both the Civil War and of any battle in American military history, claiming over 50,000 combined casualties. Union Major General George Meade's Army of the Potomac defeated attacks by Confederate General Robert E. Lee's Army of Northern Virginia, halting Lee's invasion of the North and forcing his retreat.