Roughly 180,000 black soldiers served, about 9 percent of all Union forces. The vast majority were from slave states. In joining up, they risked re-enslavement, or worse, if captured by Confederate forces. In the end, they helped smash the slave system that had held many of them in bondage shortly before their military service.

Of course, the South fashioned a new system of racial repression. At the outset of World War I, W.E.B. Du Bois strongly supported black enlistment, in the hopes that the sacrifice would lead to better treatment. “Let us, while this war lasts, forget our special grievances and close our ranks shoulder to shoulder with our own white fellow citizens,” he wrote.

African Americans made up more than 200,000 of the 2-million-strong American expeditionary force. But they got more respect from French commanders, who trained and put them on the front lines, than their own commanders. And they returned home to race riots and lynchings.

The dashed hopes of black soldiers throughout much of our history make their faithfulness all the more extraordinary.