The only Americans, other than American Indians, who ever experienced extended, large-scale enemy occupation were the people of the Confederate South. The "enemy" was the U.S. army, which set forth in 1861 to conquer the Confederacy and force the seceded states back into the Union. Over the next four years, the Union army occupied large sections of the Confederacy, especially in Virginia, Tennessee, and Arkansas, along the Mississippi River, and on the Atlantic coast. Many important Southern cities were captured, including Nashville, New Orleans, and Atlanta. Union troops in the invaded regions eventually numbered over half a million.

When the Civil War began, Northerners, including President Abraham Lincoln, believed that most Southerners were not "Rebels" at heart, but instead had been deceived into supporting secession by scheming politicians. The initial Union policy toward citizens of the occupied regions was therefore conciliatory, aimed...