All the men of Shechem assembled themselves together, and all the house of Millo, and went and made Abimelech king, by the oak of the pillar that was in Shechem.
Evidently Abimelech felt that Gideon’s other sons were ambitious to be king too, though there is no indication in the text that any of them felt this way. He was perhaps projecting his feelings on them, as is often true of ambitious people. They sometimes become paranoid, as Abimelech did (cf. King Saul).