Grossman reflects on the historical role of the leaders. Earlier I mentioned the difference between the Greek phalanx and the Roman manipulus. He writes about this in this chapter. In short:
In the Greek phalanx the leader at squad and platoon level was a spear-carrying member of the masses. The primary function of these leaders (as defined by their equipment and lack of mobility within the formation) was to participate in the killing. The Roman formation, on the other hand, had a series of mobile, highly trained, and carefully selected leaders whose primary job was not to kill but to stand behind their men and demand that they kill.
Many factors led to the military supremacy that permitted the Romans to conquer the world. For example, their volleys of cleverly designed javelins provided physical distance in the killing process, and their training enabled the individual to use the point and overcame the natural resistance to thrusting. But most authorities agree that a key factor was the degree of professionalism in their small-unit leaders, combined with a formation that facilitated the influence of these leaders.