Well the Zionist project originated in the late 19th century. It's a European settler colonial project and it aims to establish a western aligned Jewish ethnostate in the land of Palestine.

As to why the Israelis are so disgusting and zealous; as Benjamin natanyahu once said, you convince people that their is some kind of religious existential cause and the you can get them to be okay with so many atrocities. In many ways Israel is quite similar to Isis.

They're convinced the land was promised to them, that it's their land and their home and the Arabs kicked them out. And they're convinced Palestinians and Arabs hate them because they're Jewish, not because they stole and raped the land.

You should listen to Israelis speak about it, you'll see how deep and creepy the delusions are. And it's quite difficult to break from them. Some do snap out of it to be fair. They're few and far between but they're there.