In his historic play The Melting Pot, Israel Zangwill (1864-1926) introduced into our discourse a potent metaphor that for nearly a hundred years has served as a key definition of the United States. The play, enthusiastically espoused by President Theodore Roosevelt, to whom it was dedicated, offered a grand vision of America as a dynamic process of ethnic and racial amalgamation. By his own admission, The Melting Pot grew out of Zangwill's intense...