 Economic development was largely centred in Aden, and while the city flourished partly due to the discovery of crude oil on the Arabian Peninsula in the 1930s, the states of the Aden Protectorate stagnated.Encouraged by the rhetoric of President Nasser of Egypt against British colonial rule in the Middle East, pressure for the British to leave grew.Following Nasser's creation of the United Arab Republic, attempts to incorporate Yemen in turn threatened Aden and the Protectorate.