C. F. Keil and Franz Delitzsch on Judges 9:21

Jdg 9:21

But Jotham fled to Beer, after charging the Shechemites with their iniquity, and dwelt there before his brother Abimelech (“before,” i.e., “for fear of.” - Jerome). Beer in all probability is not the same place as Beeroth in the tribe of Benjamin (Jos 9:17), but, according to the Onom. (s. v. Βηρά), a place eight Roman miles to the north of Eleutheropolis, situated in the plain; at present a desolate village called el Bîreh, near the mouth of Wady es Surâr, not far from the former Beth-shemesh (Rob. Pal. ii. p. 132).

Abimelech’s reign lasted three years. ויּשׂר, from שׂוּר to govern, is used intentionally, as it appears, in the place of ויּמלך, because Abimelech’s government was not a monarchical reign, but simply a tyrannical despotism. “Over Israel,” that is to say, not over the whole of the twelve tribes of Israel, but only over a portion of the nation, possibly the tribes of Ephraim and half Manasseh, which acknowledged his sway.