Most history sources say "invaded Palestine" or "entered Palestine" when speaking of the Arab armies. Of course this took place after the mandate left Palestine.
The 1949 UN armistice agreements called the place Palestine and referenced Palestine's international borders.
Even the UN resolution 3236 of 1974 states:
So, who told you that Palestine did not exist?
Those history books and armistice agreements of 1948-1949 used the nomenclature 'Palestine' from habit - what that unchartered, unincorporated region had been called for a long time. Rather like 'Arabia', versus 'Saudi Arabia'.
But none of that means shit.
The split second that the Jews of Old Palestine declared Statehood and Independence, citing UN 181 as part of their basis, they implicitly declared new borders between themselves (the new State of Israel, per the 1947 UN proposal) and vestigial Rump Palestine; what was left of Palestine after the Jews carved-off their slice.
The Jews made their claims stick (operative in the Real World).
You failed to make your claims stick (operative in the Real World).
Hell, you were months late (September 1948) to even TRY to declare, and really didn't actually pull that off for another 40 years (1988).
Asleep at the switch.
Again.
The Illinois territory was a different critter than the State of Illinois.
The region called Cheecagong was a different critter than the incorporated City of Chicago.
The Louisiana Purchase Territory was a different critter than the State of Louisiana.
The unincorporated region formerly known as Palestine is a different critter than the fragmented and failing State of Palestine (more like, Rump Palestine).
Feel the burn.
Enjoy the burn.
'Cause you ain't gettin' the rest back.
Not in 66 years.
Not in 122.
Not in a thousand.
Time to pack it up and head for greener pastures.
It's over.