1950 and remained relatively high until 1970, after which it declined, reaching about 40 percent in 1990, the lowest level in a century. 12 One reason for this decline is the preponderance among the foreign-born of those who have only recently arrived, and who therefore do not have the requisite years of residence. A second reason seems to lie in the historically low rate of naturalization of Mexican immigrants, who have dominated recent immigration but who have tended to be sojourners. A related factor is that the U.S. foreign-born population now includes a greater number of nonimmigrants who are not eligible to naturalize. As residence of the foreign-born in general lengthens and, as seems likely, more Mexican immigrants seek naturalization, the number of applications will rise and the proportion of the foreign-born who are naturalized citizens will expand.
Several factors may account for the propensity to naturalize. One study of immigrants from all countries who became permanent resident aliens in 1971 reveals that, by 10 years after immigration, 30 percent had naturalized (Jasso and Rosenzweig, 1990:109-115). Among immigrants from Asia, Europe, Africa, and Oceania, the proportion was much higher, at 45 percent, and it was much lower among immigrants from Canada, the Caribbean, and Latin America—only 20 percent of whom became citizens within 10 years. Canadian and Mexican immigrants had particularly low rates.
Gender also plays a role. Adult men, aged 21 to 55 years, are more likely to become citizens than are women, according to census data (Jasso and Rosenzweig, 1990:107-121). Inasmuch as men generally take the lead in sponsoring family members for immigration, this difference may reflect the incentive men have to improve their standing as sponsors of their immediate families. Immigrants from English-speaking countries (other than Canada) are more likely to naturalize than are those from other countries, suggesting that language facilitates integration into U.S. society. Citizenship is one marker of the eventual assimilation of an immigrant into American society. Although rates of naturalization are at an all-time low, mainly due to Mexican immigrants, the evidence is that propensities to naturalize are now increasing rapidly, in part due to the added benefits attached to citizenship. Citizenship is not an issue for the descendants of immigrants, all of whom are citizens at birth.
Questions about immigration often focus on the potential adverse consequences on American society because of their numbers, geographical concentra-
Census data provide information about naturalization, allowing us to calculate the proportion naturalized of current foreign-born residents. These data must be treated with some caution, however, because some foreign-born residents, such as students on nonimmigrant visas, are enumerated in the decennial census but are not eligible for naturalization.