By 1961, their intractable ideological differences provoked the PRC's formal denunciation of Soviet communism as the work of "revisionist traitors" in the USSR.[1] For the countries of the Eastern Bloc, the Sino–Soviet split was a question of who would lead the revolution for world communism, and to whom the vanguard parties of the world would turn for political advice, financial aid, and military assistance: to China or to Russia?[4] In that vein, the USSR and the PRC competed for the leadership of world communism through the vanguard parties native to the countries in their spheres of influence.[5]