The Federation of Arab Emirates of the South was an organization of states

State (polity)

A state is an organized political community, living under a government. States may be sovereign and may enjoy a monopoly on the legal initiation of force and are not dependent on, or subject to any other power or state. Many states are federated states which participate in a federal union...

 within the British

British Empire

The British Empire comprised the dominions, colonies, protectorates, mandates and other territories ruled or administered by the United Kingdom. It originated with the overseas colonies and trading posts established by England in the late 16th and early 17th centuries. At its height, it was the...

 Aden Protectorate

Aden Protectorate

The Aden Protectorate was a British protectorate in southern Arabia which evolved in the hinterland of Aden following the acquisition of that port by Britain in 1839 as an anti-piracy station, and it continued until the 1960s. For administrative purposes it was divided into the Western...

 in what would become South Yemen. The Federation of six states was inaugurated in the British Colony of Aden on 11 February 1959. It subsequently added nine states and, on 4 April 1962, became known as the Federation of South Arabia

Federation of South Arabia

The Federation of South Arabia was an organization of states under British protection in what would become South Yemen. It was formed on 4 April 1962 from the 15 protected states of the Federation of Arab Emirates of the South. On 18 January 1963 it was merged with the crown colony of Aden...

. This was joined by the Aden Colony on 18 January 1963.