So why did the incumbents declare "war", huckleberry?
Who gave the land to the United Nations to "partition"?
a). A ruler or rulers would declare: here are the borders of my country, kingdom, property, etc.
b). The friendly neighbors would almost always disagree. If they thought they can win, they would attack.
c). The winner would say again: here are my borders.
Repeat b) and c) until there is no disagreement anymore.
After establishment of League of Nations, and then United Nations, the good tone became to ask the approval first. Nevertheless, Israel had to go through the steps b) and c) anyway. You might be upset with the whole process, but it how it happened always, we just personally don't care about the old ages, but care about the history we witness.
In regards of the whole Mideast region: as you know, it was under the Ottoman Empire rule for centuries up until the end of World War I, when British and French took over the control. They've drawn the borders of Iraq, Syria, Saudi Arabia, Transjordan to satisfy local strongmen they supported.