https://www.un.org/unispal/history2/origins-and-evolution-of-the-palestine-problem/part-i-1917-1947/
The defeat of the Ottoman Empire following World War I by the Triple Entente, mainly Britain and France, set the British on the path to figuring out how to benefit their empire by controlling the territory and going after its resources. The Balfour Declaration, written by British Foreign Secretary Sir Arthur James Balfour, was a statement of sympathy to the aims of Zionism, which aimed to establish in Palestine a national home for the Jewish people. Balfour's declaration also included some idealistic goals, one being that "nothing shall be done which may prejudice the civil and religious rights of existing non-Jewish communities in Palestine, or the rights and political status enjoyed by Jews in any other country."
Obviously, there was a realization that since only a very small number of Jews were resident in Palestine itself, with most of the Jewish population being scattered across Europe, and in other Arab provinces of the Middle East, the creation of a Jewish state in Palestine could result in the displacement of the Arabic population that had lived in Palestine for centuries, and it also could result in the expulsion of Jewish populations from the other countries where they existed as an ethnic and religious minority. If an independent Jewish state was established, then some countries, especially where anti-Semitism was running high, might consider Jews as foreign nationals rather than citizens, and expel them.
Empires can do as they please. I don't know if the reasoning was to allow slow, gradual Jewish immigration into Palestine, so that adjustment could be made to their presence by the Arabic population already there, and perhaps some measure of acceptance, or to use the Jewish presence to further their own interests. I'm not convinced that, under the right circumstances, with progressive, tolerant indigenous leaders in charge, that a single, democratic state could not have existed in Palestine under which both Jews and Arabs could live in peace. Up to this point in the history of the world, human intellect and reason has not been educated enough to become powerful or effective enough to bridge deep-seated religious differences and allow people to live side by side, sharing the same land, in peace.
The idea that there's something in history entitling one group of human beings to take the land, property and prosperity of another is the root of the problem. But trying to solve problems by war or terrorism is ineffective, immoral and inhumane. It's been tried now for 75 years. Maybe both sides are tired enough of the results to try something different now.
= new reply since forum marked as read