The British conquered Aden in 1839 and it was then known as the Aden Protectorate. The British also made a series of treaties with local tribal rulers, in a move to colonise the entire area of southern Yemen. British influence extended to Hadhramawt by the 1950s and a boundary line, known as the "violet line" was drawn between Turkish Arabia in the north and the South Arabian Protectorate of Great Britain, as it was then known. (This line later formed the boundary between northern and southern Yemeni states in the 1960s.)
In 1849 the Turks returned to the Yemen and their power extended throughout the whole of that region not under British rule. Local insurrection against the Turks followed and autonomy was finally granted to the Zaydi imam in 1911. By 1919 the Turks had retreated from the Yemen for the last time and the country was left in the hands of Imam Yayha, who became the country's king. Yemen's independence was recognised by Britain in 1925.