The Sages taught: Converts are not accepted in the days of the Messiah. Similarly, they did not accept converts in the days of King David or in the days of King Solomon. Rabbi Eliezer said: What is the verse that hints at this halakha? “Behold, they may gather together [gor yagur], but without Me; whosoever shall gather together [gar] with you shall fall on yours” (Isaiah 54:15). The word gor implies that
only a convert [ger] who becomes part of the Jewish people when the Jews are living in exile, at a time when God is not clearly revealed, i.e., “without Me,” are considered part of the Jewish people.
But another who wishes to convert in a time when God is clearly revealed shall not be accepted.
Yevamot 24b:8
Some rabbis held that intermarriage would only be forbidden if the non-Israelite party to the marriage does not convert, but others held that converting them in order to marry is also forbidden."[8]
Some Tannaim [writers of the talmud] look at the story of Solomon marrying Pharaoh's daughter and declare it a "criminal act."[9]
There is also a discussion on Judaism's policy (which is found in the Talmud at Yevamos 24b) of forbidding conversion unless the "Jewish people is downtrodden."[10] R' Shlomo Ganzfried outlines the policy saying that "during the reigns of King David and King Solomon
, when the Jews enjoyed political autonomy and financial prosperity, no converts were accepted, since they were likely to be motivated by a desire for personal security and monetary gain. Likewise, proselytes will not be accepted in the Messianic era."[10] This is held not to be the case with Pharaoh's daughter, as "
the Talmud explicitly states that this did not apply to the daughter of Pharaoh, who had enough wealth not to need to marry Solomon for money (Talmud Yevamos 76a)."[8]
Pharaoh's daughter (wife of Solomon) - Wikipedia
Other sources:
Mothers of Israel: Why the Rabbis Adopted a Matrilineal Principle
Karaite Judaism - Wikipedia
(patrilineal Jews who only follow the written word)
Radhanite - Wikipedia
(an example of some jewish men who moved around a lot and probably spawned
several confused groups of Indian, Chinese, etc semi Jews who are currently fighting to be recognized by a very strict, very rabbinical Israel)