South Yemen was a socialist state until 1990. In 1980, Abdul Fatah Ismail, founder of the Yemeni Socialist Party is reported to have resigned. No details. He is said to have left Yemen. On his return there was a civil war of short duration between his supporters and the supporters of his succesor Ali Nasir Muhammad, which led to the death of Ismail and the proposed deposition of Ali Nasir.
The People’s Democratic Republic of Yemen and the Yemen Arab Republic, north and south, merged in 1990. Details unknown.
Southern Yemen has a British colonial history owing to the 17th Century. The Front for the Liberation of occupied Yemen and the Marxist National Liberation front were both contingents for Yemen in the 1960’s. The consequences of the 1967 Arab-Israeli war, the six day war, were many casualties and an end to the front for occupied Yemen, resulting in a socialist state:
It is said to be proposed oil drilling in north Yemen is the reason for a planned merger, but violent outbreaks from the north resulted in said intervention from the Arab league in 1979.
Since 2007 northerners have again been actively seeking independence. Northern Houthis are loyal to deposed president Ali Abdullah Saleh who served as president until 2012. He was assassinated in 2017.