John Brown's raid on Harpers Ferry, Virginia (now West Virginia), is often considered to be a defining moment that led to the start of the Civil War.
Brown led an uprising on October 16-18th, 1859 as a means to start an armed slave revolt across the south. Although this attempt can be said to have failed, leading to his execution shortly thereafter, the widely publicized nature of this uprising is often said to have directly influenced events that followed- ultimately leading to the Civil War and the ending of slavery.
Today, Harpers Ferry is a National Historical Park and the history of John Brown's uprising is preserved for all to see.
But beyond visiting for the history, Harpers Ferry itself is simply a gorgeous town located on the confluence of the Potomac and Shenandoah Rivers and is also at the dividing point between three states (Maryland, West Virginia, and Virginia). So as much as you should be visiting this one for its history, you'll also want to explore here for the scenery too!