After the Great War, the Ottoman Empire made a very bad decision; they decided to side with the Central Powers in World War I. It was thought that the Turks really had no choice in this. If the Allied Powers won the war then Britain, France and Russia would take hold of the straits at Turkish expense. And when the Ottoman Empire aligned themselves with Germany (one of the Central Powers) instead of the Allied Powers, they allowed for just that to happen.
The three powers (Britain, France, and Russia) within the Allied Powers began to break-up the Ottoman territory amongst themselves in secret agreements that gave Russia control of the straits, gave Syria and Lebanon to France and promised most of present-day Iraq and Jordan to Britain, and projecting an international power in Palestine.
Great Britain also started what was known as the “Arab Revolt” within the Ottoman Empire in order to try and speed-up the end of Ottoman Empire. They did this by going after Ottoman-appointed governor of the holy cities, the Sharif of Mecca, Husayn ibn Ali, head of the Hashemite dynasty and thirty-seventh in direct descent from the Prophet Muhammad (s.a.a.w). In secret negotiations, the British promised to Husayn their support of an Arab state or states under Hashemite rule in the Arabian peninsula, Syria, Iraq and in the Hashemite interpretations, Palestine (great debate with what the English word “district” referred to.
Clearly the British have now put themselves in a lot of trouble seeing that most of this land has already been promised in another secret negotiation to France.
Moreover, this was not the last promise that the British had made in the Middle-East. Britain was involved in an catastrophic World War and thus the Brits were trying to win over the Zionist movement. They thought that if they were to win over the Zionist movement than they would be winning over the Jewish support in Russia and in the United States and possibly gaining an ally in the future grounds of the Middle East. So Britain went forward and promised in secret that Palestine will be the national homeland for Jews. This was known as the Balfour Declaration.