This Article proposes a new account of how empire became constitutional. When the United States took a deliberate imperial turn in 1898-1899 by annexing Puerto Rico and the Philippines, many jurists thought that the Constitution automatically made these islands proto-states and their residents U.S. citizens with full constitutional protections. Three decades later, this expansive view was no longer mainstream. Contrary to standard accounts, this momentous change was neither quick nor the result of unilateral judicial action. To perceive dynamics extending beyond the judiciary, this study examines the attempts to win U.