The so-called West Bank is the West bank of the Jordan River, and the West bank of the Dead Sea. The 'original' (pre-'67) borders were established by a UN ceasefire line in 1949, when it was obvious that the then Palmach was about to exterminate the British backed Arab Legion. A quick cease fire was called to save some segment of British authority in the region.
The West Bank has a natural defensive border on the river, much like another border, called the Rio Grande, where the land on the North side of that river was taken from another country.
The Brits, by the way, have NEVER liked the idea of Israel, and have done their level best to destroy it, from the beginning, up to and including stripping all the kibbutzs of weapons as they pulled out of Palistine and giving the guns to the Arabs in Jordan, Syria, and Egypt.
If Israel has no right to the West Bank, then by the same reasoning, we should give Texas, New Mexico, Arizona and California back to Mexico, with improvements. How is your Spanish?
I was in Israel about 20 years ago and was shocked when I saw the "mighty" Jordan. ;^)
You could easily cross it by jumping from rock to rock for about 50 feet.