One critical factor that led to the Mfecane was the

Explanation

The war-created refugee problems is the correct answer. Refugee problems created by the wars is one of the major factors that led to the Mfecane, e.g. when Zwide attacked Sobhuza it led to the Ngwane moving their place in the Pongola valley and into an unknown region where they became invaders and raiders looking a new homeland to build the Swazi composite.