Question

what caused the muslim army to grow over the course of the war?
the muslims captured people from other tribes and then forced them to fight in the army.
there were traitors in the meccan army who came over to the muslim side.
people began to believe that god was helping the muslim army so they joined them in the fight.
rewatch

Explanation:

Historically, in the context of early Islamic expansion, the growth of the Muslim army was often attributed to the religious - motivated belief among people that divine support was with the Muslim forces, leading them to voluntarily join. Forcing captured people to fight was not a common or primary reason for army growth, and while defections could occur, the main driver was religious - inspired enlistment.

Answer:

People began to believe that God was helping the Muslim army so they joined them in the fight.