Relationships between the PCI and the Soviet Union gradually fell apart as the party moved away from Soviet obedience and Marxist–Leninist orthodoxy in the 1970s and 1980s and toward Eurocommunism and the Socialist International. The PCI sought a collaboration with Socialist and Christian Democracy parties (the Historic Compromise). However, Christian Democrat party leader Aldo Moro's kidnapping and murder by the Red Brigades in May 1978 put an end to any hopes of such a compromise. The compromise was largely abandoned as a PCI policy in 1981. The Proletarian Unity Party merged into the PCI in 1984.