ESA, the European Space Agency, is (formally) independent of other international cooperations like the European Union. After the fall of the Soviet Union, were there ever any proposals for ESA to join with the Russian space agency? ESA does accept new smaller member states now and then, including the former Soviet republic of Estonia in 2015. In the 1990s Roscosmos had big financial problems but also world leading space competence and assets. Among them the flight ready Energia/Buran launch system. There seems to have been potentially great synergies with such a merger.
Also, Ukraine and Kazakhstan had important space industries and assets, so I'd like to include them in this question.