Albert Barnes Commentary Judges 9:3

"And his mother`s brethren spake of him in the ears of all the men of Shechem all these words: and their hearts inclined to follow Abimelech; for they said, He is our brother." — Judges 9:3 (ASV)

The Ephraimite pride revolted from Abi-ezrite rulers, and inclined them to one who was a Shechemite by birth (compare the same spirit in the time of David and Rehoboam, 2 Samuel 20:1; 1 Kings 12:16).