We are dealing with a mass murder who lust for power blinded him to love, mercy, and justice.
Abimelech ruled for three years. He is not counted as a king of Israel, however, because he was not anointed, he made no claim to be faithful to God, and his claim to a throne was directly contradictory to the governmental system of Israel at the time, that of prophets and tribal judges. He was a despotic and tyrannical ruler, and he quickly lost the support of those who had originally made him king.
You can build a throne with bayonets, but you can’t sit on it for long.” – Boris Yeltsin
Abimelech sought to rule over Shechem by eliminating all his opposition—namely, by killing all the other sons of Gideon (Judges 9:1–2). All were killed except Gideon’s youngest son, Jotham (Judges 9:5). Abimelech then became king of Shechem (Judges 9:6).