Of the many themes that characterize U.S. history, immigration is oneof the most constant and most pervasive. Since the first European andAfrican immigrants began arriving in North America during the earlyseventeenth century, immigrants have steadily poured into what is nowthe United States. During the early twenty-first century, that flow hascontinued unabated - the major difference being that most immigrantsnow come from Latin America - especially Mexico and Central America- and Asia. Of the 281,421,056 residents of the nation counted by theU.S. Census in 2000, nearly 99 percent traced their ancestry toimmigrants who arrived here within in the past four centuries. Moreover, even Native Americans - who make up the remainder - can trace theirancestry to immigrants who came thousands of years earlier. TheUnited States is, indeed, a nation of immigrants