Two-thirds of the Palestinian Mandate was set up as an Arab Muslim state (Palestinian) in 1921 by the British, with a Saudi Prince as its King. The rest of the mandate belongs to Israel.
Even the original Trans-Jordanian ruler (the current ruler's grandfather)stated that his country was Palestine. I believe (correct me if I'm wrong)that he was assassinated for that statement on the Temple Mount
The problem is that the rest of the Arab world, and now the entire Muslim world believes that once an area is conquered by Islam, it remains their land forever. They forget (even though their own Koran states that Israel belongs to the Jews), that the land was given by God to Israel as an inheritance.
Mandate for Israel in 1920Land given to the Muslims.
Land given to Israel by YHvH