The story of the United States is not just one of expansion, but also of territories lost or given up over time. From sun-drenched islands in distant oceans to lands once claimed across the continent, the U.S. has held—and then released—a surprising array of lands. How did these regions come under American control? What prompted their transfer, independence, or sale? In exploring these lost American lands, we uncover remarkable tales of diplomacy, ambition, and the lasting impact these territories have had on both the U.S. and the world.