The men of Shechem set liers-in-wait for him on the tops of the mountains, and they robbed all who came along that way by them: and it was told Abimelech.
In other words, he's an outsider. We ought to be serving Hamor and his family, let them be the kings. And he said to God the people were under my rule, because I can really do a good job here, you know. Who's Abimelech? And so he said if you would just commit yourself to me I would remove Abimelech.