John Gill Commentary 2 Chronicles 15:6

"And they were broken in pieces, nation against nation, and city against city; for God did vex them with all adversity." — 2 Chronicles 15:6 (ASV)

And nation was destroyed of nation, and city of city
Or one tribe of another; as the Ephraimites by the Gileadites, and the tribe of Benjamin by the other tribes; and Shechem by Abimelech, (Judges 9:45) (12:6) (Judges 20:21Judges 20:24Judges 20:44–48) ,

for God did vex them with all adversity ;
both with foreign enemies and civil wars; and now it is intimated that this would be their case again, should they not keep close to the Lord their God.