> Zionists purchased land in the region and immigrated legally

Colonial Britain famously sold a lot of land they didn't control, occupy or reasonably administrate. The Raj comes to mind.

The Balfour Declaration, in context, was like buying a car title from the impound lot. The slip of paper might say you own it, but nobody ever notarized it at the DMV. And now the person who put 50,000 miles on the odometer is going to see you in court for the rest of their life.