America was born as an immigrant nation. It went through many periods of nearly unlimited immigration, coupled with xenophobic backlashes when particular groups - Germans, Jews, Irish, Mexicans, or Poles - came in such numbers and so abruptly that the traditional powers of assimilation were for a time overwhelmed. But the eras of ethnic ghettoes and tribal separatism were usually brief, given the inclusive popular culture and official government efforts to overwhelm identification with the home country.