World War I (“The Great War”) toppled empires, created new nations, and sparked tensions that would explode across future years. On the battlefield, gruesome modern weaponry wrecked an entire generation of young men. The United States entered the conflict in 1917 and was never again the same. The war heralded to the world the United States’ potential as a global military power, and, domestically, it advanced but then beat back American progressivism by unleashing vicious waves of repression. The war simultaneously stoked national pride and fueled disenchantments that burst Progressive Era hopes for the modern world. And it laid the groundwork for a global depression, a second world war, and an entire history of national, religious, and cultural conflict around the globe.