Gambrill Mill, Monocacy Civil War Battlefield
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American Civil War -- In Summer 1864 U.S. Grant's National Army had Robert E. Lee's Rebel Army trapped near Richmond Virginia, and William Sherman's National Army was "marching [rampaging] through Georgia" heading for South Carolina. So in time, barring a nasty miracle, the industrial northern United States was going to defeat the agricultural secessionist southern Confederacy. But that miracle nearly happened!!

A small Confederate army outmaneuvered a poorly-led National army in the Shenandoah Valley of Virginia, and invaded Maryland and turned toward Washington DC. National General Lew Wallace [later of Ben Hur fame] gathered a scratched-together, outnumbered force of regulars, reserves, and invalids; and fought a bitter delaying action on the banks of the Monocacy River 50 miles (80 kilometers) northwest of Washington DC. Wallace's force was defeated and scattered, but the Confederate army was delayed for nearly a full day. It then marched on through Maryland to assault the previously unmanned defenses of Washington. But the Confederate attack came only an hour after veteran National troops sent by ships from Grant's army disembarked to successfully garrison Washington's defensive forts They got there just in time. (and as a spectator Abraham Lincoln nearly got himself shot). One or two hours changed history-that-could-have-been.

Thus, repulsed in an attempt to invade the Capital of the United States, the Confederate army eventually retreated back into Virginia; on the way, they demanded ransoms from towns in Maryland and southern Pennsylvania, and burned Chambersburg Pennsylvania in retaliation for Nationalist depredations in the Shenandoah Valley, Virginia ...

And the American Civil War then bloodily proceeded to the now inevitable Confederate surrender.