Brezhnev offered Transylvania to Hungary

Hungarian Communist leader Janos Kádár's aeroplane pilot told him in 1971 that Leonid Brezhnev had suggested Hungary take back Transylvania. 

"The plan ultimately unravelled because Hungarian leadership feared the dire economic conditions in the region would be too heavy a burden."

In 1968 Brezhnev considered invading Romania after conquering Czechoslovakia and Harold Wilson's cabinet may have gone to war with Communist Russia if this happened. 

(By the way, England previously might have gone to war with Russia over what is now Romania shortly before we went to war with her over control of the holy sites in Jerusalem.)