“When the men of Judah raised the battle cry, God routed Jeroboam and all Israel before Abijah and Judah.”
(2 Chronicles 13:15 HCSB)

The men fought the battle.  God routed Jeroboam and all Israel.

The writer of Chronicles is concerned about first causes, not second causes.

What, dear reader, do you assume you are responsible for doing, that God brought about?  (Hint:  Everything).