Deuteronomy 23:7 "You must never seek their peace nor their prosperity all your days, forever"
The nations of Ammon and Moab are to be totally rejected.
As we mentioned above (Negative Mitzvah 53), the Torah explains that their very nature is cruel.
When the Jewish people were on their way out of Egypt, they did not offer any hospitality or answer requests for even a bit of bread and water. Additionally, they hired Balaam to curse the Jewish people.
This Negative Mitzvah concerns war with Ammon or Moab.
In general, we are commanded to offer the opportunity of peaceful surrender to enemy cities in times of war. However, this offer of peace may not be made to Ammon and Moab.
To Rob, Toronto According to Maimonides, "When Sannecherib, King of Assyria, arose, he confused the identity of all the nations, mixing them together, and exiling them from their place... Since the forbidden nations became intermingled with all the nations of the world [with] whom it is permitted [to marry once they convert], all [converts] are permitted. For when anyone of them separates himself [from them by] converting, we operate under the presumption that he became separate from the majority." So we don't know today who are Ammonites or Moabites.
In any case, these nations neighbored the Land of Israel, while the Arabians lived much further away in Arabia, so it is doubtful that they are the same.