By the late 1950s, an earlier proposal to federate some of the smaller statelets had grown into a much broader scheme to include all of the principalities and sheikhdoms into a larger political entity that would eventually achieve independence.
Britain's insistence that Aden be a part of the new entity created the anomaly that eventually killed the plan. The sophisticated business community, the activist trade unions, and other similarly modern political and social organizations in Aden feared for their future at the hands of what they perceived to be a group of largely illiterate and parochial tribal leaders from the rural areas of the protectorates. The tribal leaders, on the other hand, feared at worst their overthrow, or at best a degree of political and economic participation severely limited by an Adeni population that included many non-Muslims and non-Arabs.
The British continued to insist upon their chosen course of action, and by 1965, all but four of the 21 protectorate states had joined the "federation." Shortly thereafter, Britain announced that independence would ensue no later than 1968. This announcement unleashed the violent political conflict that prevailed in Aden and the protectorates for the next two years as sundry organizations fought for control of the destiny of South Yemen...
The establishment of a republic in North Yemen provided a tremendous incentive to the elements in the south that sought to eliminate the British presence there. Furthermore, the Egyptians agreed to provide support for some of the organizations campaigning for southern independence--e.g., the Front for the Liberation of South Yemen (FLOSY). However, not all elements in either of the two Yemens were sympathetic to Egyptian policies, much less to the dominant role that Egypt had begun to play in southwestern Arabia. An emergent alternative movement, the National Liberation Front (NLF), drew its support primarily from indigenous sources. As the time for independence drew near, the conflict between the various groups, and especially the NLF and FLOSY, escalated into open warfare for the right to govern the state after British withdrawal. By late 1967, the NLF clearly had the upper hand; the British finally accepted the inevitable and arranged the transfer of sovereignty to the NLF on Nov. 30, 1967.