Complex sentence: On September 23,1949, the USSR detonated its first atomic bomb; and on October 1,1949, the Communists in China prevailed in the Chinese Civil War and declared a communist state.
Split into simpler sentences: On September 23,1949, the USSR detonated its first atomic bomb. And on October 1,1949, the Communists in China prevailed in the Chinese Civil War and declared a communist state.