Ahmad bin Yahya
In the 20th century, Imam Yahya Muhammad Hamid ed-Din, King of the Mutawakkilite Kingdom of Yemen (North Yemen) attempted to realize these aspirations but only managed to consolidate his control in Upper Yemen, Lower Yemen, Marib, and Lower Tihamah. He expressed his claim to Aden and the Aden Protectorate in treaties, such as in the Italo-Yemeni Treaty of 1926. He was forced to acknowledge Saudi control over Asir and was unable to dislodge the British from the Aden hinterland or Hadhramaut. British control of Aden was also challenged by his successor King Ahmad bin Yahya who did not recognise British suzerainty in South Arabia and also had ambitions of creating a unified Greater Yemen. In the late 1940s and the early 1950s, Yemen was involved in a series of border skirmishes along the disputed Violet Line, a 1913 Anglo-Ottoman demarcation that served to separate Yemen from the Aden Protectorate.