The people were naturally unhappy with how they were treated. On top of the burdensome tribute, they had to endure taunts and physical harassment. It is not at all surprising that they sought deliverance, nor that they sought it through a military means. After all, they had achieved notable military success, previously beating back Lamanite advances and, mostly recently, having successfully ambushed an army and put it to flight. Given their concentrated pleading, it is also not surprising that Limhi gave permission for the military effort.