The Battle of Perryville, also known as the Battle of Chaplin Hills, was fought on October 8, 1862, in the Chaplin Hills west of Perryville, Kentucky, as the culmination of the Confederate Heartland Offensive (Kentucky Campaign) during the American Civil War. Confederate Gen. Braxton Bragg's Army of Mississippi initially won a tactical victory against primarily a single corps of Maj. Gen. Don Carlos Buell's Union Army of the Ohio. The battle is considered a strategic Union victory, sometimes called the Battle for Kentucky, since Bragg withdrew to Tennessee soon thereafter. The Union retained control of the critical border state of Kentucky for the remainder of the war.

On October 7, Buell's army, in pursuit of Bragg, converged on the small crossroads town of Perryville in three columns. Union forces first skirmished with Confederate cavalry on the Springfield Pike before the fighting became more general, on Peters Hill, when the Confederate infantry arrived. Both sides were desperate to get access to fresh water. The next day, at dawn, fighting began again around Peters Hill as a Union division advanced up the pike, halting just before the Confederate line. After noon, a Confederate division struck the Union left flankthe I Corps of Maj. Gen. Alexander M. McCookand forced it to fall back. When more Confederate divisions joined the fray, the Union line made a stubborn stand, counterattacked, but finally fell back with some units routed.Buell, several miles behind the action, was unaware that a major battle was taking place and did not send any reserves to the front until late in the afternoon. The Union troops on the left flank, reinforced by two brigades, stabilized their line, and the Confederate attack sputtered to a halt. Later, three Confederate regiments assaulted the Union division on the Springfield Pike but were repulsed and fell back into Perryville. Union troops pursued, and skirmishing occurred in the streets until dark. By that time, Union reinforcements were threatening the Confederate left flank. Bragg, short of men and supplies, withdrew during the night, and continued the Confederate retreat by way of Cumberland Gap into East Tennessee.Considering the casualties relative to the engaged strengths of the armies, the Battle of Perryville was one of the bloodiest battles of the Civil War. It was the largest battle fought in the state of Kentucky.

The American Civil War (April 12, 1861 – May 9, 1865; also known by other names) was a civil war in the United States between the Union (states that remained loyal to the federal union, or "the North") and the Confederacy (states that voted to secede, or "the South"). The central cause of the war was the status of slavery, especially the expansion of slavery into territories acquired as a result of the Louisiana Purchase and the Mexican–American War. On the eve of the Civil War in 1860, four million of the 32 million Americans (~13%) were enslaved black people, almost all in the South.The practice of slavery in the United States was one of the key political issues of the 19th century. Decades of political unrest over slavery led up to the Civil War. Disunion came after Abraham Lincoln won the 1860 United States presidential election on an anti-slavery expansion platform. An initial seven southern slave states declared their secession from the country to form the Confederacy. Confederate forces seized federal forts within territory they claimed. The last-minute Crittenden Compromise tried to avert conflict but failed; both sides prepared for war. Fighting broke out in April 1861 when the Confederate army began the Battle of Fort Sumter in South Carolina, just over a month after the first inauguration of Abraham Lincoln. The Confederacy grew to control at least a majority of territory in eleven states (out of the 34 U.S. states in February 1861), and asserted claims to two more. Both sides raised large volunteer and conscription armies. Four years of intense combat, mostly in the South, ensued.

During 1861–1862 in the war's Western Theater, the Union made significant permanent gains—though in the war's Eastern Theater the conflict was inconclusive. On January 1, 1863, Lincoln issued the Emancipation Proclamation, which made ending slavery a war goal, declaring all persons held as slaves in states in rebellion "forever free." To the west, the Union destroyed the Confederate river navy by the summer of 1862, then much of its western armies, and seized New Orleans. The successful 1863 Union siege of Vicksburg split the Confederacy in two at the Mississippi River. In 1863, Confederate General Robert E. Lee's incursion north ended at the Battle of Gettysburg. Western successes led to General Ulysses S. Grant's command of all Union armies in 1864. Inflicting an ever-tightening naval blockade of Confederate ports, the Union marshaled resources and manpower to attack the Confederacy from all directions. This led to the fall of Atlanta in 1864 to Union General William Tecumseh Sherman and his march to the sea. The last significant battles raged around the ten-month Siege of Petersburg, gateway to the Confederate capital of Richmond.

The Civil War effectively ended on April 9, 1865, when Confederate General Lee surrendered to Union General Grant at the Battle of Appomattox Court House, after Lee had abandoned Petersburg and Richmond. Confederate generals throughout the Confederate army followed suit. The conclusion of the American Civil War lacks a clean end date: land forces continued surrendering until June 23. By the end of the war, much of the South's infrastructure was destroyed, especially its railroads. The Confederacy collapsed, slavery was abolished, and four million enslaved black people were freed. The war-torn nation then entered the Reconstruction era in a partially successful attempt to rebuild the country and grant civil rights to freed slaves.

The Civil War is one of the most studied and written about episodes in the history of the United States. It remains the subject of cultural and historiographical debate. Of particular interest is the persisting myth of the Lost Cause of the Confederacy. The American Civil War was among the earliest to use industrial warfare. Railroads, the telegraph, steamships, the ironclad warship, and mass-produced weapons saw wide use. In total the war left between 620,000 and 750,000 soldiers dead, along with an undetermined number of civilian casualties. President Lincoln was assassinated just five days after Lee's surrender. The Civil War remains the deadliest military conflict in American history. The technology and brutality of the Civil War foreshadowed the coming World Wars.