Jewish immigration was encouraged by European leaders and European Jewish groups between 1900-1940. As Jews came in they developed irrigation systems, electrical grid, created farms and industry, and Arabs came to work the land and factories and build their own too. My main point, however, is that it is not "stolen" land, the Palestinians are not 2000+ year old people. They came to the land from different places and from different tribes in the Arab world just like the Jews came from the UK and Poland and Germany etc - and most of them roughly from the same period of time.
Exactly, the Arab population in those years grew much more by natural increase than by immigration.
But not many, not even 1/10th of the numbers that live there today.
Something like that is true of many parts of the world. The last two centuries were the time of the population explosion.