Notwithstanding efforts by others to resolve these disputes and promote some measure of accommodation, the basic conflicts appeared irreconcilable. In fact, South Yemen helped to instigate and fund a broad-based opposition movement in the north, the National Democratic Front. The South Yemenis perceived their cause--that of Marxist transformation of the Arab political, economic, and social systems--to be in desperate need of direct action; accordingly, elements of the leadership sanctioned the assassination of the North Yemeni president in 1978. At the same time, they supported other revolutionary organizations in the region, such as the Popular Front for the Liberation of Oman (PFLO). The continuing friction thus engendered led to another brief war, in 1979, which was followed by new efforts on the part of other Arab states to bring about a reconciliation (in order to avert intervention by the Great Powers). All the while, however, significant fissures--both ideological and practical--were opening within the Yemen Socialist Party (YSP). 'Abd al-Fattah Isma'il was the major ideologue of the NLF and was the driving force behind the organization's move toward the Soviet Union as well; he succeeded the president who had been held responsible (and executed) for the 1978 assassination, Salim 'Ali Rubayyi.