Was there not an original plan, going back to when Israel first got independence, to have Jordan BE the REAL Palestinian nation? Hey even the Jordan flag for example looks very much like the proposed Palestinian one.
In the 1947 United Nations Partition Plan ... which the Jewish representatives of the future nation of Israel fully supported - Jordan was not even in the picture, in any way, shape or form.
Jordan was cut out of the picture in the early Palestine Mandate days with the League of Nations, during the San Remo Conference, where they finalized the Palestine Mandate. That was in the early 1920s.
IIRC, that was what was proposed in the Balfour Declaration after World War I. No one got around to the actual creation of a Jewish state (the whole of Israel and Jordan remained “the Palestinian Mandate”) until after World War II when the horrors of the Holocaust were revealed, and then Israel was roughly divided by an “X”, with the north and south sectors Jewish and the east and west sectors Arab.