John Gill Commentary 2 Chronicles 17:1

"And Jehoshaphat his son reigned in his stead, and strengthened himself against Israel." — 2 Chronicles 17:1 (ASV)

And Jehoshaphat his son reigned in his stead
In the stead of Asa his father:

and strengthened himself against Israel ;
the ten tribes, by fortifying his cities, building castles, raising and keeping a large standing army, as the latter part of this chapter shows, and the next verse.