Just look up the history of Israel before it was given statehood and of Zionism. Here is a good article by the Guardian. warning, it's a very complicated situation, all in all, and this article really gets into the nitty gritty of history. Literally, deep into it. It's some heavy reading.

Boiled down though...

After the defeat of the Ottomans and their empire partitioned off to various countries after the Sinai and Palestine campaigns of WW1, the British were given control via a mandate by the League of Nations over a territory that became known as the Mandate of Palestine, but it was still mostly Arab citizens, the British were just given authority to maintain order in the region.

During the years of occupation, the British government encouraged European Jews to settle the region in an effort to fulfill political obligations to the Zionist movement made at what is known as the Balfour Declaration. This caused a civil war to break out over the whole colonization thing.

With the end of the Mandate over the region drawing to an end, and the tensions of the area heightened after civil war, the U.N. voted to subdivide the Mandate of Palestine into two separate states: Palestine and Israel