The Colony of Aden was divided into an eastern colony and a western colony. Those were further divided into 23 sultanates and emirates, and several independent tribes that had no relationships with the sultanates. The deal between the sultanates and Britain detailed protection and complete control of foreign relations by the British. The Sultanate of Lahej was the only one in which the sultan was referred to as His Highness. The Federation of South Arabia was created by the British to counter Arab nationalism by giving more freedom to the rulers of the nations.

Two states:

The revolution in the north coincided with the Aden Emergency, which hastened the end of British rule in the south. On 30 November 1967, the state of South Yemen was formed, comprising Aden and the former Protectorate of South Arabia. This socialist state was later officially known as the People’s Democratic Republic of Yemen and a program of nationalization was begun.
Relations between the two Yemeni states fluctuated between peaceful and hostile. The South was supported by the Eastern bloc. The North, however, was not able to get the same connections. In 1972, the two states fought a war. The war was resolved with a ceasefire and negotiations brokered by the Arab League, where it was declared that unification would eventually occur. In 1978, Ali Abdullah Saleh was named as president of the Yemen Arab Republic. After the war, the North complained about the South’s help from foreign countries. This included Saudi Arabia. In 1979, fresh fighting between the two states resumed and efforts were renewed to bring about unification.