The Unification of Saudi Arabia was a military and political campaign in which the various tribes, sheikhdoms, city-states, emirates, and kingdoms of most of the Arabian Peninsula were conquered by the House of Saud, or Al Saud. Unification started in 1902 and continued until 1932, when the Kingdom of Saudi Arabia was proclaimed under the leadership of Ibn Saud, creating what is sometimes referred to as the Third Saudi State, to differentiate it from the Emirate of Diriyah, the First Saudi State and the Emirate of Nejd, the Second Saudi State, also House of Saud states.