This means that God applied the curse Jotham made by sending an evil spirit to cause trouble and animosity between Abimelech and the leaders of Shechem.
# God did this so the violence done ... helped him murder his brothers
The passive phrases can be stated in active form. AT: "God did this to avenge the seventy sons whom Abimelech their brother murdered and the men of Shechem helped murder" (See: [[rc://en/ta/man/translate/figs-activepassive]])