Remember the battle of Zama when the Romans shouted in unity with each other while the Carthaginian mercs rabble gave from themselves some incohorent sounds.

Imagine how it would be to control such army IF Hannibal Barca were not there.

I agree though that such unity is nonexistent if the soldiers are only some device to profit the rich elite rather than in fighting some rational war against tyranny (like Allies in WW2).