The Fulfilment of the Curse on Abimelech and Shechem (Judges 9:22-57).
‘ And Abimelech was prince over Israel for three years.'
Three is the number of completeness. His full reign was short. ‘Three years' could mean one and a half years upwards. By ancient reckoning a part of a year was counted as a year.
Note that he was ‘made prince' over Israel and not king. Only Shechem accepted him as ‘king'. But seemingly his accession after the death of Gideon was now accepted by those over whom Gideon had been prince, and his power was such that they did not wish to dispute it. ‘Over Israel' indicates being prince over some part of Israel. It meant he was prince over some of God's people who were an essential part of the whole.
The whole narratives make clear to anyone of any intelligence that he was not appointed king over Judah, the independent tribe to the south who were rarely called to arms, or over the prickly and jealous Ephraim, so concerned for their own position, or over Transjordan who would not even supply food to Israel's army. Even a so-called naive writer would have been aware of that. But in fact they were not naive, they simply counted a part as the whole as the whole book demonstrates. To rule over a part was to rule over ‘Israel'. For a part of Israel to be subjected was for the whole to be subjected. How else were three or four combined tribes to be briefly described?