Jarom 1

 Jarom again reiterates - 

"...we multiplied exceedingly, and spread upon the face of the land, and became exceedingly rich in gold, and in silver, and in precious things, and in fine workmanship of wood, in buildings, and in machinery, and also in iron and copper, and brass and steel, making all manner of tools of every kind to till the ground, and weapons of war—yea, the sharp pointed arrow, and the quiver, and the dart, and the javelin, and all preparations for war.

9 And thus being prepared to meet the Lamanites, they did not prosper against us. But the word of the Lord was verified, which he spake unto our fathers, saying that: Inasmuch as ye will keep my commandments ye shall prosper in the land."  (Jarom 1:8–9)

I believe this promise still holds today.