What is "Ach Nifsha mi'Kiryas Oz"?
Nazir 23a: This refers to Lot, who separated from Avraham; "And quarrels (keep him out) like a bolt on a fortress" teaches that he instigated quarrels (that keep out his descendants) like a bolt on a fortress - "an Amoni or Mo'avi will not marry into the congregation of Hashem." (These nations descend from Lot.)
Rashi: There is a brother who sinned against his brother, and via his rebellion he lost a city of strength, e.g. Lot against Avraham, and Esav against Yakov.
R. Yonah: Verse 18 praised a lottery for ceasing quarrels and coveting. It is common for brothers to divide property that they inherited from their father. How much they must beware of monetary quarrels, lest they come to hatred! A brother who sins and rebels against his brother is harsher than a strong city. I.e. one who brother rebels against his brother is harsher than hatred of all men of a strong city. A brother is more prone to damage, for he knows his brother's affairs and how he can harm him. Nifsha is like Poshe'a; its grammatical form is like Nishba. Also Nilcham is like Lochem.
Malbim: Sometimes a brother has a share in an inheritance, and he is sure of his rights like a strong city - "Hon Ashir Kiryas Uzo" (11). He sins against his brother and expels him from his inheritance. Quarrels and judgments close against him like a bolt on a fortress that is closed well, and does not allow anyone to enter. Via the quarrel and judgment it is very hard to attain his desire and enter the city that he sinned against it. Therefore, it is good to end [the quarrels] via a lottery - "b'Cheik Yutal Es ha'Goral ume'Hashem Kol Mishpato" (16:33).
What is "Midyanim ki'Vri'ach Armon"?
Nazir 23a: Lot instigated quarrels (that keep his descendants out) like a bolt on a fortress - "Lo Yavo Amoni u'Mo'avi bi'Khal Hashem" (Devarim 23:4).
Rashi: Arguments between them separate them forever, like a bolt used to lock gates of a fortress, so one cannot enter.
R. Yonah: Quarrels between brothers are harsher and stronger than a bolt that locks the doors on a fortress. No one can open the doors from outside and break the bolt. So no one can find an opening to make Shalom between brothers, for there is strong hatred between them. The rebellion and betrayal of a brother reaches the Nefesh more than betrayal of a stranger.
Malbim: Refer to 18:19:1:4.
