This statement seems to have been included to explain the reason why the Israelites had been reduced to this state.
Then was war.
The Hebrews were given no peace. The Canaanites began to attack the Israelite walled towns, hemming in the people. Evidently the Canaanites, like the Philistines later, had proscribed the trade of the smith and all armament making among the Hebrews, so that there was hardly an effective shield or spear among 40,000 men of military age. This policy effectively eliminated any danger of retaliation by the Hebrews.