The Japanese General in 1942 - What's the Difference?

Special kind of entity maybe a warrior so if you're playing Japan for example during a certain period you may be allowed to build a unique sort of a unit called a samurai. If you're playing Scandinavian's during a certain era you might be able to build a certain unit called a Viking. These are units that are a facet of the culture and that's why these societies get them another society's done but again what is that game mechanics element representing?