Background
In March 1991, Mikhail Gorbachev, the president of the Soviet Union, proposed a federation by holding a referendum to preserve the Union as the Union of Sovereign States. The new treaty signing never happened as the Communist Party hardliners staged an attempted coup in August that year. Often considered as the successors of the USSR, it is one of the largest intergovernmental organizations in Europe.
https://en.wikipedia.org/wiki/Commonwealth_of_Independent_States