What Is the Plus Four Bonus in Warfare?

The psychological advantage that happens after many victories would begin to build up in a battle between say Vikings and Franks. One side disadvantaged psychologically before the combat even starts now it's worth asking another key question about this special ability. Is it really a special ability or is it something that everyone has in warfare just turned up to a very high amplitude? Are we talking about something as simple and basic as morale here because as everyone knows morale is a key element in warfare go read your son su go read your claus with the military maxims of so many generals.