The TL;DR is that after WW2 and the horrors of what the Nazis (not Germans, Nazis) got up to, there was a brief intense soul searching in the rest of the world (which was quite happily anti semitic before the war) that maybe things had got a little out of hand.
Hence the revival of the Balfour declaration and a kind gesture by Britain (as the main occupier of Palestine at the time) to give away other countries land to make up Israel as a permanent home for the Jewish people.
Obviously the people in these occupied lands had no say in how this unfolded (you can see where Trump gets his ideas abut Ukraine from).
I am well aware this is insultingly simplified to the point of not really being much use. However I don't think there is anyone on the planet who can be said to truly understand the Middle East. (Maybe) least of all anyone who lives there.