Immigration was sharply reduced by restrictionist laws in the 1920s and plummeted further in the Depression decade of the 1930s, which saw the lowest population increase -- only 7 percent -- in American history. But this turned out to be a brief chapter. Contrary to almost universal expectations, post-World War II America was an era of boisterous economic growth and of a baby boom that began just after the war and lasted for about 20 years.
Americans were jostled out of their home states by the war and then continued moving, with huge flows to the West and, particularly after the civil rights movement got rid of racial segregation, to the South. California grew from 6.9 million to 10.6 million in the 1940s and 20 million in 1970; Texas from 6.4 million in 1940 to 11.2 million in 1970, and Florida from 1.9 million to 6.8 million in those years.
Demographers in the late 1960s expected the future to be like the recent past. They waited for the children of the baby boom to produce a new baby boom and discounted the likelihood of mass immigration. But a new chapter was beginning around 1970. Birth rates plummeted, and immigration -- mainly from Latin America and Asia -- surged.
The move to the South and West continued: In 2000, California had 34 million people, Texas 20.9 million, Florida 16 million. Hispanics now outnumber blacks.
Recently, we've seen signs of a new chapter. Divorce and abortion rates are down, and fertility rates are up, far higher than in other affluent nations. Democrats look for gains from Hispanics, Republicans in fast-growing exurbs (97 of the 100 fastest-growing counties since 2000 voted for George W. Bush in 2004). The lesson of the past is that America keeps changing and growing, often in ways we fail to anticipate.