Like other American research universities, Northwestern was transformed by World War II. Franklyn B. Snyder led the university from 1939 to 1949, when nearly 50,000 military officers and personnel were trained on the Evanston and Chicago campuses. After the war, surging enrollments under the G.I. Bill drove drastic expansion of both campuses. In 1948 prominent anthropologist Melville J. Herskovits founded the Program of African Studies at Northwestern, the first center of its kind at an American academic institution. J. Roscoe Miller's tenure as president from 1949 to 1970 was responsible for the expansion of the Evanston campus, with the construction of the lakefill on Lake Michigan, growth of the faculty and new academic programs, as well as polarizing Vietnam-era student protests. In 1978, the first and second Unabomber attacks occurred at Northwestern University. Relations between Evanston and Northwestern were strained throughout much of the post-war era because of episodes of disruptive student activism, disputes over municipal zoning, building codes, and law enforcement, as well as restrictions on the sale of alcohol near campus until 1972. Northwestern's exemption from state and municipal property tax obligations under its original charter has historically been a source of town and gown tension.
 In 1938, what famous attacks occured at Northwestern?