In the summer of 1917, at docks up and down the eastern seaboard, thousands of American soldiers boarded ships bound for France. They were the vanguard of a new American army, about to enter the most destructive war the world had ever known. For President Woodrow Wilson, the war was a crusade “to make the world safe for democracy,” a chance to transform the international order in America’s image. But it was a war that the United States had resisted entering for more than two years—and one that would unleash consequences and new realities that we live with to this day.