After a coup in 1960 mounted by neutralist forces, Souphanouvong became actively engaged in negotiations resulting in an international conference on Laos in 1961-62, and the formation of another coalition government headed by his half-brother in which healso served. That conference failed to end the civil war in Laos, whose fortunes were linked closely with the more important conflict in neighbouring Vietnam. Souphanouvong continued to be involved in negotiations with his half-brother's adm i nistration, which led eventually to a third coalition government in 1973; it failed to survive the success of revolutionary communism in Vietnam and Cambodia in 1975.