Because firstly, it had originally been the Jewish homeland hundreds of years before, prior to occupation by Arab armies in the expansion of Islam and the domination of the territory by the Ottoman Empire. Secondly, the land had been granted to them by the British Empire, as it had been part of Britain's territories since the end of the First World War, so the Jewish government in Israel when first established in 1948 had total international legitimacy. Thirdly, after losing 6 million of their people during the Holocaust, the survivors felt a need to leave Europe and join forces in a land where they would not be slaughtered en masse; their Holy Land seemed like a good choice at the time.
Hope that I helped!
