It was the war that changed everything, and yet it's been mostly forgotten: in 1935, Italy invaded Ethiopia. It dominated newspaper headlines and newsreels. It inspired mass marches in Harlem, a play on Broadway, and independence movements in Africa. As the British Navy sailed into the Mediterranean for a white-knuckle showdown with Italian ships, riots broke out in major cities all over the United States.

Italian planes dropped poison gas on Ethiopian troops, bombed Red Cross hospitals, and committed atrocities that were never deemed worthy of a war crimes tribunal. But unlike the many...