Since its foundation in 1948, the State of Israel has had to determine how they will treat the “Jewishness” of certain groups. Whether or not a person is treated as a Jew has several practical applications, but in Israel the most important difference is marriage. Because the religious Rabbinate controls marriages in the country, they do not perform marriages between Jews and non-Jews. Thus, determining whether or not someone is Jewish makes a huge difference.
The first major group in question were the Karaites. Rabbi Tzvi Pesach Frank fought very strongly to not allow the Karaites to be considered Jews in the new Jewish state, but not because they are not Jewish. Everyone agrees that they are. Rather, the Rama (EH 4:37) says that it is not permitted to marry a Karaite because they must all be treated as safek mamzerim. The reason for this is fairly logical. Since they get married with kiddushin but don’t give a proper get, any children from “second marriages” would inherently be illegitimate.
Karaites, however, are distinct from any other group of Jews whose status as Jews might be in question. This is because Karaites always had some greater connection to the Jewish community. Thus, whether or not a person was actually a Karaite (and therefore a descendant of the initial Karaites who were definitely Jews) was never really in question. Yes, some non-Karaites may have joined the community over the centuries, but as a general rule we can rely on the majority that someone who comes from Karaite communities is a Jew.
It is a big dispute among poskim whether or not (and in what circumstances) we believe someone we don’t recognize who comes and says that he is Jewish. Many poskim believe that you would need two Kosher witnesses to come and say that he is Jewish in order to accept him as a Jew. This requirement creates potential problems, especially for someone coming from an area containing are no Kosher witnesses. And even if you don’t require witnesses, what happens when you can’t believe someone or think he’s mistaken about being Jewish in the first place?
The former was the question that the major poskim in Israel had to deal with when Jews were finally allowed to leave in the 1990s. People fled the dying Soviet Union en masse, and there were reports of many who claimed to be Jewish just so they would be allowed into Israel. Also, many of these Russian immigrants were not able to participate in any form of Jewish community whatsoever and had no way of proving that they were Jewish. Even if we would usually believe any person who claims to be Jewish, in this case it is difficult to do so because there was reason to believe that people who really aren’t Jewish might be lying to get into the country. In the end, most of the poskim agreed that the halacha is that we believe someone who claims to be Jewish. Nevertheless, most Russian immigrants underwent a giyur lechumra, a conversion just to be safe.
The Russian controversy, however, is entirely different than a long pre-existing question that re-emerged when the State of Israel was founded. What about African tribes that seemingly have Jewish roots? The major question is about the Ethiopian communities, but it applies to a few other African groups as well.
Jews in Europe and Israel knew about the Ethiopian community since at least the 16th century. The Radbaz in a responsum (Divrei David 5) says that without a doubt these tribes are Jews from the lost tribe of Dan and that they must be treated as such. Nevertheless, he ends off by saying that one should be careful about who they marry because maybe they have kiddushin and then got divorced without a proper get (the same issue that the Rama mentioned regarding the Karaites).
R’ Ovadia Yosef, in a seminal t’shuvah (Yabia Omer 8 EH 11), ruled based on this Radbaz that not only must the Ethiopians be treated completely as Jews, but that they may even marry any Jew without undergoing any sort of giyur lechumra. R’ Ovadia was able to say this because, in his very next t’shuvah, he rejects the Rama’s ruling about the Karaites. He says that it is permissible to marry the Karaites and that we should do our best to teach them about Orthodox Judaism so that they will accept the Oral Torah as well as the Written one (quoting Rambam Mamrim 3:3).
The Tzitz Eliezer, who in his responsa (5:17 and other places) fought very strongly against the Karaites being permitted to marry Jews, disagrees with this ruling of R’ Ovadia. He uses quite a poetic language throughout his responsa to describe how the Jews have always followed the Rama in never marrying Karaites. In 12:66, he quotes the former Ashkenazic chief Rabbi of Israel, Rabbi Yitzchak Isaac Halevi Herzog, who questioned the entire premise of the Radbaz. He wonders whether the Radbaz was correct to begin with and says that even if he was, how do we know that things did not change over the next 500 years? In fact, he points out that the more lenient you are about calling them Jews, the stricter you will have to be about allowing them to marry Jews. Thus, while making them convert might be considered insulting, it would allow them to marry any Jew they wish. The Israeli Rabbinate, in a controversial decision just a few years ago, decided to be safe and required the Ethiopian immigrants to undergo a giyur lechumra in deference to the opinion of R’ Hertzog and against R’ Ovadia.
What about other African tribes that seem to have Jewish roots? Actually, there is not much written about them. Presumably the ruling of the Radbaz would not apply to them because, well, he wasn’t talking about them when he said that certain groups are definitely from Dan. Does this mean that we assume they aren’t Jewish at all? Far be it from me to decide such an important issue, but presumably we would take the fact that they are similar enough to Jews to assume that they have some Jewish ancestry. Thus, unless we know that historically they were never Jews, we would probably only require a giyur lechumra and not a full conversion.