When is "Acharis ha'Yamim"?
Radak: It is in the days of Mashi'ach. The same applies to returning "Shevus Bnei Amon" (49:6). And so it says in Tzefanyah (2:9) about these two nations "She'eris Ami Yevazum v'Yeser Goyi Yinchalum." This wa said due to their pride. They reviled and were haughty against Am Hashem Tzevakos, like it says above "Ki Al Hashem Higdil" (verse 26). It says there (2:11) "Ki Razah Es Kol Elohei ha'Aretz v'Yishtachavu Ish mi'Mekomo Kol Iyei ha'Goyim." This will be only in the days of Mashi'ach. Even though the nations were mixed up, perhaps they were scattered to places close to their land. Even though they were mixed among other nations 1 , perhaps some memory of them remains.
Brachos 28a: Yehudah Ger Amoni was permitted to marry a Yisraelis because Amon was exiled, and became mixed among the nations. We assume that he came from the majority of nations, which are permitted.
Will only Mo'av return in "Acharis ha'Yamim"?
Radak: Every nation will return to its land, and all will be under the rule of Yisrael - "Edom u'Mo'av Mishlo'ach Yadam u'Vnei Amon Mishmatam" (Yeshayah 16:2).
Why does it say "Ad Henah Mishpat Mo'av"?
Radak: It is because the Navi elaborated about them. "Mishpat" means that the decree against them is justified.
Malbim: Also in the Nevu'ah about Amon, it mentions the destruction of Cheshbon and Ai (49:3), cities of Mo'av, but there it was said regarding Amon's punishment. Also Sefer Yechezkel mentions Mo'av's fall at the time of Amon's fall. Until here was Mo'av's punishment due to itself, and not due to others.
