Had reigned - Rather, "had ruled." It is not the phrase used in Judges 9:6. It looks as if the Shechemites alone had made him king, and the rest of Israel had submitted to his dominion, without allowing his title of king.

When Abimelech had reigned three years over Israel. The people in general consenting to what the men of Shechem had done, at least not opposing it, all being desirous of a king, and therefore put up with a mean person, rather than have none; though it is amazing they should, and that they had not rose up as one man against Abimelech, and avenged the blood of the sons of Gideon, who had been so useful and serviceable to them; it is indeed said that he reigned over all Israel, and his reign, such as it was, was very short, as is often the case with wicked princes.

Abimelech is seated in the throne his father refused. But how long does this glory last? Stay but three years, and see the bramble withered and burned. The prosperity of the wicked is short and fickle. The Shechemites are plagued by no other hand than Abimelech's. They raised him unjustly to the throne; they first feel the weight of his sceptre.

GAAL'S CONSPIRACY. (Judges. 9:22-49)
When Abimelech had reigned three years--His reign did not, probably at first, extend beyond Shechem; but by stealthy and progressive encroachments he subjected some of the neighboring towns to his sway. None could "reign" in Israel, except by rebellious usurpation; and hence the reign of Abimelech is expressed in the original by a word signifying "despotism," not that which describes the mild and divinely authorized rule of the judge.

Abimelech's reign lasted three years. ויּשׂר, from שׂוּר to govern, is used intentionally, as it appears, in the place of ויּמלך, because Abimelech's government was not a monarchical reign, but simply a tyrannical despotism. "Over Israel," that is to say, not over the whole of the twelve tribes of Israel, but only over a portion of the nation, possibly the tribes of Ephraim and half Manasseh, which acknowledged his sway.

Over Israel - For though the men of Shechem were the first authors of Abimelech's advancement, the rest of the people easily consented to that form of government which they so much desired.