He stationed troops in every fortified city of Judah and put garrisons in the land of Judah and in the cities of Ephraim that his father Asa had captured.
Here we find concerning Jehoshaphat, I. What a wise man he was. As soon as he came to the crown he strengthened himself against Israel, Ch2 17:1. Ahab, an active warlike prince, had now been three years upon the throne of Israel, the vigour of his beginning falling in with the decay of Asa's conclusion.
Commenting on 2 Chronicles 17:1-9
And he placed forces in all the fenced cities of Judah,.... A considerable number of soldiers, to defend them should they be attacked: and set garrisons in the land of Judah: on the frontiers and borders of it, to protect it: and in the cities of Ephraim; soldiers to keep garrison there: which Asa his father had taken; see Ch2 15:8.
The cities of Ephraim - This conquest from the kingdom of Israel is referred to, Ch2 15:8; but when it was made we do not know.