Sometimes the Door Slams Shut

% For most of its history, the U.S. has been wide open to immigrants -- those from Europe, that is. Countless 19th century voyagers from the Old World pursued the uniquely egalitarian shelter of a New World so different from Europe's rigidly structured nation-states. Barriers to immigration did not square with the American ideal of opportunity for all.

Not that each newcomer was welcomed by a fledgling society entirely free from fear and bias. In 1798 Congress raised the residency requirement for citizenship from 5 to 14 years, largely to exclude political refugees from Europe who might foment revolution. Later some...