During the San Remo Conference at the end of WWI, the Mandate system was created to redraw the map of the Middle East, which was until then colonized by the Ottoman Turks who would lose all their colonies.
The San Remo Resolution, adopted on April 25, 1920, by the Supreme Council of the Principle Allied Powers, under the auspices of the League of Nations, put into force the Balfour Declaration of 1917 – which until then had only been an expression of British policy – and gave it standing in international law.
The San Remo Resolution set aside all of what was then known as Ottoman Palestine for the creation of a homeland for the Jewish people. But in 1922, when the Mandate for Palestine was actually implemented, the eastern part (all the land east of the Jordan River), which represented 73% of Palestine, was hived off to create another Arab state which would become the Kingdom of Jordan. This in fact was the first ‘Two-State Solution’, leaving the Jewish people with only 27% of Palestine. It should be recognized as well that the legitimacy of the present Arab states of Syria, Iraq, Jordan and Lebanon derives from the same international law that reconstituted the Jewish nation-state of Israel.
The purpose of the Mandate for Palestine, as stated in the Preamble (3rd paragraph) was to “reconstitute the national home of the Jewish people”, based upon the historical connection of the Jews to the land of Israel (Palestine).