Also, to complicate the issue a little more. Mandate Palestine includes all Israel, the Territories, and Jordan. Jordan was the first state carved out of Palestine. The remainder was then made subject to a UN partition plan the Arab Palestinians rejected. They declared war and lost in 1948.
This particular issue of Israel v Palestine is not the best example of the sanctity of borders.
The UN Charter declares all member states to have "territorial integrity" that cannot be altered by war. "Once a state always a state" is the rule. The rare exceptions are when countries dissolve under the principle of self-determination into multiple states like Yugoslavia. And more recently Kosovo. However, in those instances you did not see the acquisition of territory by one state over another.