Local militias offered the Song a way to obtain large numbers of troops cheaply. Their training and availability could not match those of professional soldiers. Fighting capable enemies such as the Mongols required a force that could be used reliably, while the scale of the threats also demanded sufficient numbers. The difficulty was deciding how much manpower to buy cheaply and how much to maintain as a professional army.
Notable Point · 40:19-41:26
Cheap militia numbers and professional readiness
Local militias reduced costs, while professional soldiers provided the training and readiness needed against capable enemies.