The rise of McCarthyism took place in the context of increased fears that communists had infiltrated the highest levels of the US government, including the State Department and even the armed forces. In 1950, the Soviet Union successfully tested an atomic bomb, and China, with the world's largest population, became a communist nation. One prominent member of the Manhattan Project testified that he had been a Soviet spy, and Julius and Ethel Rosenberg were convicted of espionage. These events, as well as the conflict in Korea, helped create an atmosphere of fear that McCarthy skillfully stoked to his own political advantage. In this atmosphere, his allegation that he knew of hundreds of Communists working in the State Department, the statement that vaulted him to national prominence, seemed more believeable, and more of a threat than it would have at another time. It is important to note that McCarthy was not the only purveyor of anti-Communist hysteria at the time. Hundreds of loyalty boards, anti-American activities investigation committees, and citizen's watch programs existed at every level of government.