Among the people that the Torah teaches cannot join the Jewish people through marriage are Egyptians and people from the nations of Edom, Ammon and Mo’av (see Devarim 23:2-5). The Mishna teaches that there are differences between them, however. Egyptians and Edomites who convert will be allowed to marry only other converts for three generations, after which they can marry anyone. Amon and Mo’av can never join the Jewish people through marriage, although women from those nations can convert and marry immediately.
Do these rules apply in the modern age?
Already in the time of the Mishna (see Massekhet Yadayim 4:4) there was an awareness that the ancient people could no longer be considered direct descendants of the countries in which they lived. We find tanna’im like Rabbi Akiva and Rabbi Yehoshua, who told prospective converts from these nations that King Sanherib of Assyria exiled people from their lands to such an extent that we cannot possibly know from what nation someone descends. For this reason, the rule limiting converts from marrying into the Jewish people was not applied.
Nevertheless, our Gemara tells of Minyamin, an Egyptian convert who was a student of Rabbi Akiva’s, who shared his plan of marrying off his children and grandchildren to other converts so that they would eventually be allowed to freely marry. Many rishonim understand that there is a need to distinguish between the nations to the north and east of Israel, who were dispersed by Sanherib and Nevuhadnezzar, and Egypt, which was more successful in retaining a national identity throughout history.
In fact, we find two conflicting statements in the Tosefta, one of which suggests that the prophetic statement guaranteeing the return of the Egyptian nation to its land lends credence to the possibility that the people living in Egypt are truly Egyptians. Nevertheless, the Rambam rules that all of the nations have moved from one place to another and that we can no longer really know who is who. According to this ruling, none of the Torah’s rules about these nations apply any longer.