Shalom Rabbis, The Oral Torah (Gemara-Sanhedrin 58a-b) establishes which are the binding sexual prohibitions for the Gentiles. Rambam, in Hilchot Melachim 9: 5 encodes them synthetically as follows: There are six illicit sexual relations forbidden to a gentile: a) his mother; b) his father’s wife; c) a married woman; d) his maternal sister; e) a male; f) an animal. From this list of prohibitions it is clear that, for the purposes of incest, the paternal lineage is irrelevant for the Goym, only the maternal one is relevant. And in fact, the sister for the fathers part alone is granted to the goy man, as Gemara and Rambam himself deduce from the interpretation of the passage from Genesis 20:13, in which Abraham says about his wife Sarah: “And also, indeed, she is my sister, the daughter of my father, but not the daughter of my mother, and she became my wife.” Now, the Halachic rulings of the Gemara on this matter seem to me to be consistent with each other; however, in my studies a difficult reconciliation of the aforementioned halakhah with what we read in the Written Torah has emerged,in my opinion . In fact, in the eighteenth and twentieth chapters of Leviticus, HaShem orders to the sons of Israel a series of sexual prohibitions much wider than those established for the Gentiles by the Gemara; in the same chapters, HaShem clearly states that he expelled the Canaanite peoples from the Promised Land precisely because they practiced these "abominations". Now, I ask myself: but if HaShem punished the Canaanites, who were Goym, for such acts, He evidently previously forbade them these behaviors, otherwise on what legal and moral principle were the Canaanites punished for practicing these behaviors? "Nullum crimen sine lege " (one is only punished for that which he was commanded/obligated) said the ancient Romans, and this is also a principle of the Halakhah, "For whoever does these things is an abomination to the Lord; and because of these abominations, the Lord your God is driving them out from before you” (Deuteronomy 18:9–12). Evidently, the Canaanites were punished for these practices; and since God would not have punished them for an action unless He first prohibited it, these practices are clearly prohibited to gentiles. How do we reconcile the sexual prohibitions established by the Written Torah in Leviticus 18 and 20, the violations of which determined the divine punishment for the Canaanites, towards whom therefore HaShem must have pronounced a previous prohibition ("nullum crimen sine lege", as stated in previously) with the much more limited sexual prohibitions for Gentiles set out in the Oral Torah (Gemara -Sanhedrin 58 a-b) and codified in Rambams Mishneh Torah -Hilchot Melachim 9: 5? I apologize for the length of the letter, I could not be shorter. Shalom

Thanks for your question. The Canaanites apparently did all (!) of the those aforementioned actions (Leviticus 18, 24 and 27), including those which are forbidden to Noachides, and for which they were punished. True, the Land of Israel is originally meant for the People of Israel, and accordingly, demands that higher level of morality, and cannot stand any abominations. Nevertheless, you are correct that the Canaanites were just punished for those prohibitions for which they (!) were obligated [which may be why the Torah lists immediately beforehand (v. 22-23) precisely the prohibitions of homosexuality and bestiality, as they are particularly "abominations" and "wickedness", and for which even the Canaanites are also obligated, and transgressed, which led to their expulsion].