In addition to his military duties, Sassou-Nguesso became increasingly active in politics. He came to be considered a protégé of President Marien Ngouabi, who ruled from 1968 until 1977. President Ngouabi appointed Sassou-Nguesso to the position of minister of defense in 1975. Soon afterwards, Sassou-Nguesso was named to a special revolutionary staff. In 1977, he became vice president of the PCT military committee. In that same year, President Ngouabi was assassinated and succeeded by Sassou-Nguesso's rival, Joachim Yhombi-Opango, a former chief of staff. Yhombi-Opango was more sympathetic toward the West than the former Marxist regime. Economic problems, and Yhombi-Opango's attempts to resolve them, brought him into conflict with the left wing of the PCT. In February 1979, he was forced to relinquish power to a provisional committee appointed by the PCT. As president of that committee, Sassou-Nguesso was appointed president of the Republic the following month.