It is impossible to estimate exactly what weight should be given to each of the various factors which have contributed to the conflict between the Communist regimes of Russia and of China, but there can be no doubt that Russia's refusal to assist China to become a nuclear power was one of the most important. According to the Chinese account of the matter, the Soviet Union promised to provide China with “a sample of an atomic bomb and technical data concerning its manufacture,” apparently as part of an agreement on “new technology for national defence” concluded in October 1957, but went back on this promise and unilaterally annulled the agreement in June 1959. The Chinese People's Republic, nevertheless, went ahead on its own and exploded its first atomic bomb on 16 October 1964; this was followed by China's first hydrogen bomb on 17 June 1967.