 Al-Hamdi was assassinated in 1977, and his successor, former Chief of Staff Ahmed Hussein al-Ghashmi, was killed in June 1978.The lengthy tenure of President Ali Abdullah Saleh, who ruled North Yemen from 1978 until it merged with South Yemen in 1990, proved more stable.Saleh strengthened the political system, while an influx of foreign aid and the discovery of oil in North Yemen held out the prospect of economic expansion and development.