Nativism diminished at the beginning of the twentieth century. A robust national economy shielded newcomers, even as the assassination of President McKinley by Leon Czolgosz, an American-born radical, led Congress in 1903 to bar "anarchists or persons who believe or advocate the overthrow by force or violence of the Government of the United States… or the assassination of public officials." The nation's immigration bureaucracy grew quickly after 1900, boasting more than 1,200 workers by 1906. A year later Congress established the Immigration Commission, which in 1911 issued a huge report that popularized the distinction between the "old" and "new" immigration. The former was salutary, the latter baneful. The Immigration Commission also searched for illness at Ellis Island and on the West Coast, as bacterial and viral outbreaks—long associated with specific immigrant groups— became a means to distinguish "healthy" Americans from sickly aliens. In 1793, Philadelphians deemed an outbreak of yellow fever "Palatine Fever," to indicate German immigrant responsibility for the outbreak; in 1832 nativists attributed a cholera epidemic on the eastern seaboard to Irish-Catholic immigrants; and in 1900 the Chinese in San Francisco took the blame for an outbreak of bubonic plague. By 1907, in addition to anarchists, immigration undesirables excluded from American shores included paupers, polygamists, lepers, beggars, prostitutes, epileptics, victims of tuberculosis, those suspected of "moral turpitude," and imbeciles. Clearly the stigma of disease served to marginalize immigrants culturally and to remove them—indeed, often by quarantine—from society's mainstream. Only by embracing the consumer culture of personal cleanliness could newcomers exhibit patriotism and become American.
Nativism did flare in San Francisco in 1906, when the school board ordered the exclusion of Japanese children from that city's public schools. Regional prejudice quickly threatened to overturn President Theodore Roosevelt's Far Eastern policy. Long a bastion of racialism, California assumed its anti-Japanese stance naturally. The Japanese and Korean Exclusion League appeared in 1905, as Japan and Russia waged war in East Asia, and repeated charges made earlier against the Chinese, warning that the Japanese jeopardized not only the standard of living but also the primacy of the white race. Many nativists, including the novelist Jack London and publisher William Randolph Hearst, excoriated the Yellow Peril. Not only had Japan's strong showing in war against Russia made it a world power, but now its position of strength in the Far East threatened the self-image of the United States as a superior, Anglo-Saxon nation. Ironically, Japan itself had a long history of institutionalized xenophobia, but now showed concern over its international status. Tokyo protested this exclusion, which placed Washington in the awkward position of convincing Californians of their obligation to the Union, while at the same time seeking to secure equal treatment for citizens of a foreign power. Concerned at Japan's new strength in Asia and upset by riots in Tokyo protesting the Treaty of Portsmouth, which he helped negotiate, President Theodore Roosevelt moved to restore cordial relations with Tokyo.
His own racism notwithstanding, Roosevelt withstood opposition from the Pacific coast and Rocky Mountain regions—and from southern advocates of Jim Crow and states' rights. He warned that he would employ military force, if necessary, and sent a personal representative to San Francisco. Mayor Eugene Schmitz soon revoked the segregation order, and Roosevelt promised to work to place Japanese immigration on a treaty basis. The president also dispatched the navy's Pacific Fleet on a dramatic global voyage—after informing Tokyo not to view the move as an unfriendly act.
Roosevelt and the Japanese exchanged several diplomatic notes, which became the basis in 1907 for the so-called "Gentleman's Agreement," an executive agreement that restricted passage of Japanese laborers from Hawaii and Japan to the United States unless they had "already been in America." The arrangement, shifting Japanese migration to the United States from basically male to female, quieted but did not halt anti-Japanese agitation. Foreign-born Japanese ( Issei ) remained "aliens ineligible to citizenship," while second-generation citizens ( Nisei ) found the Fourteenth Amendment a poor guarantee of the rights of citizenship against discriminatory law and custom. After leaving office, Roosevelt himself concluded that cultural and economic conflict was inevitable in relations between Americans and Asians.
Nativism reached its apogee during and directly after World War I. Just prior to American intervention in the conflict, congressional restrictionists overcame President Woodrow Wilson's veto and passed the major recommendation the Dillingham Commission made six years earlier. The Immigration Act of 1917 barred illiterate adult immigrants; set a head tax of eight dollars per person; and excluded vagrants, alcoholics, advocates of violent revolution, and "psychopathic inferiors." Passage of a literacy test and the establishment of a barred zone in the southwest Pacific—which closed the gates to Asians not already banned by the Chinese Exclusion Act and Gentleman's Agreement—indicated that the Great War heralded a more sinister era in the history of American nativism.