Abimelek had an eye for the main chance, and sought to be the only ruler after Gideon's death. Abimelek sought to rule like kings of other nations. He was ruthless and even murdered all but one of his brothers.
Jotham escaped and then told the nation in parabolic style what they had done. Then he confronted the nation with its sin. All peoples have a habit of choosing bad leaders. Most notoriously in the 1930's the Germans chose Hitler, but even in democracies we have a habit of choosing those who make the nicest sounding promises. When things go wrong it is not just the leaders who are responsible, we all have a degree of responsibility. Jotham then fled the country for his own safety.
Abimelek's reign did not have peace for long. A regime founded on intrigue and treachery will fall victim to intrigue and treachery, and Abimelek was killed