In 1962, Mao Zedong and Nikita Khrushchev agreed to fuse China and the Soviet Union together, creating the Sino-Soviet Republics, a Communist superpower. They were easily the most powerful country in the world, also getting aid from Cuba (due to the ongoing missile crisis) until civil war broke out. Democratic rebels from all over the Union attempted to wrest Communist control in an attempt to make a more democratic Union. With aid from various global superpowers, the democrats ended up winning. Due to the Union being taken over by democrats, the Union dissolved into numerous smaller countries.
The Sino-Soviet Republics were essentially a superpower of superpowers. The two republics had the highest population of any country at the time. They also had a giant military, which was made even better by the Chinese technology. If any country went to war with the Sino-Soviet Republics, they'd most likely lose. However, the only war the Sino-Soviet Republics truly fought in was a civil war; which led to its downfall.