The Torah (Debarim 23:4-9) lists four nations whose members are forbidden for marriage to Jews, even if they undergo proper conversions. These are the nations of Egypt, Edom, Amon and Moab.
Does this prohibition apply nowadays? If, for example, a person living in the region that in ancient times was Moab decides to undergo a proper Halachic conversion out of a sincere desire to join the Jewish people, may a Jewish girl marry him? Or, if a modern-day Egyptian undergoes conversion, is he a Halachically-valid candidate for marriage to a Jewess, given that he was born and raised in Egypt?
The Rambam (Rabbi Moshe Maimonides, Spain-Egypt, 1135-1204), in Hilchot Isureh Bi’a (end of chapter 12), records the tradition that the Assyrian king Sanherib transferred the populations of the nations of the ancient world. Sanherib conquered many nations and brought their populations to differet lands, thus creating a "Bilbul" (literally, "confusion" or "mix-up"), whereby the residents of any given nation cannot be assumed to be the indigenous population of that country. The people living in Amon, for example, may have actually originated from Egypt, and vice-versa. Therefore, anybody living in the areas of these four forbidden nations has the status of "Safek," meaning, it is uncertain whether he originates from the nation in question, or from a different nation. We may therefore apply the Halachic principle of "Rob" ("majority"), which allows relying on a statistical majority. For example, when an Egyptian man converts to Judaism and moves to the United States, we may assume that he descends from any of the other nations, and not from the ancient Egyptians, such that he is permissible for marriage. Therefore, assuming the conversion was sincere and Halachically valid, he would be allowed to marry a Jewish girl in communities that allow marriage to converts.
An interesting question arises concerning a case of a convert from one of these countries who wishes to marry a Jewish girl in his country – for example, if an Egyptian undergoes a proper conversion and then wishes to marry a Jewish girl in Egypt. The aforementioned principle of "Rob" applies only when the person in question left his original place. We then apply the principle of "Kol De’parish Me’ruba Parish" – "Anyone who separates [can be assumed to have] separated from the majority." When he is still in his place of origin, however, we apply a different principle, called "Kol Kabu’a Ke’mehsa Al Mehsa Dami" (literally, "Anything that is fixed in its place is like a fifty-fifty probability"). This means that at the place of origin, we cannot rely on a statistical majority, and must instead treat this situation as a statistical tossup, so-to-speak. Seemingly, then, an Egyptian convert who is still in Egypt must be viewed as a "Safek," as possibly a member of the original nation of Egypt from Biblical times, and it would be forbidden to marry such a convert.
In truth, however, the Poskim rule leniently on this issue. The Torah prohibition against marrying members of these nations applies only to a "Vadai," meaning, to individuals who are unquestionably members of these nations. If there is any doubt concerning a certain individual as to whether he is part of one of these nations, then, according to Torah law, that person is permissible for marriage. Therefore, all people from these nations after Sanherib’s conquests are potentially forbidden only on the level of "Mi’de’Rabbanan" – by force of Rabbinic enactment. There is no Torah prohibition potentially involved, since the Torah prohibition applies only in situations of "Vadai." We therefore have more room for leniency, and thus, even if the Egyptian convert is still in Egypt, there are enough questions concerning his origins that we may be lenient and allow a Jewish girl to marry him.
It should be noted that, interestingly enough, the Rosh (Rabbenu Asher Ben Yehiel, Germany-Spain, 1250-1327) maintained that even after Sanherib’s conquests, one may not marry an Egyptian convert. He claimed that forty years after Sanherib exiled the Egyptian population, the Egyptians returned to Egypt, and we can therefore assume that the people of Egypt are the descendants of the ancient Egyptians to whom the Torah refers. However, the Rambam and other authorities do not accept this view, and Halacha follows their ruling, that one may marry a convert from Egypt.
Summary: The Torah forbids marrying people from the nations of Edom, Amon, Moab and Egypt even after they convert. Nowadays, however, one may marry people from those regions – including Egyptians – who convert, as we need not assume or even suspect that they descend from the original nations that lived there in Biblical times. This assumes, of course, that the conversion was Halachically valid, and that one’s community permits marrying converts.
