A vivid narrative of an ill-fated Pan American flight during World War II that captures the dramatic backstories of its passengers and, through them, the impact of Americans' global connections. On February 21, 1943, Pan American Airways' celebrated seaplane, the Yankee Clipper, took off from New York's Marine Air Terminal and island-hopped its way across the Atlantic Ocean. Arriving at Lisbon the following evening, it crashed in the Tagus River, killing twenty-four of its thirty-nine passengers and crew. Americans in a World at War traces the backstories of seven worldly Americans aboard that plane, their personal histories, their politics, and the paths that led them toward war. Combat soldiers made up only a small fraction of the millions of Americans, both in and out of uniform, who scattered across six continents during the Second World War. This book uncovers a surprising history of American noncombatants abroad in the years leading into the twentieth century's most consequential conflict. Long before GIs began storming beaches and liberating towns, Americans had forged extensive political, economic, and personal ties to other parts of the world. These deep and sometimes contradictory engagements, which preceded the bombing of Pearl Harbor, would shape and in turn be transformed by the US war effort. The intriguing biographies of the Yankee Clipper's passengers—among them an Olympic-athlete-turned-export salesman, a Broadway star, a swashbuckling pilot, and two entrepreneurs accused of trading with the enemy—upend conventional American narratives about World War II. As their travels take them from Ukraine, France, Spain, Panama, Cuba, and the Philippines to Java, India, Australia, Britain, Egypt, the Soviet Union, and the Belgian Congo, among other hot spots, their movements defy simple boundaries between home front and war front. Americans in a World at War offers fresh perspectives on a transformative period of US history and global connections during the "American Century."