Total War is the idea of taking the battle to the masses.

In the past, in the case of battles between established nations, wars were generally fought between armies. Furthermore, there were some kinds of unspoken rules to be followed: Don't butcher civillians. Don't raze cities. (well, unless you really, really have to, of course) In fact, in the past, war offered, in a way, some amusement for spectators: civillians might go up on a high hill and have a picnic while watching the two armies fighting it out from the distance. Fighting in wars was never really a civilized thing, but, like many unpleasent and nasty professions, it had some kind of unspoken set of rules.

Total war is just the opposite of this; there are no rules. In total war, civillians are butchered, cities are razed to the earth. Sometimes, the ground is even burnt and salted so nothing can ever grow again. The purpose is three fold: firstly, to destroy the war making abilities of the enemy. If their cities, factories, and the like are burnt to the ground, they can't produce any new equipment. Secondly, if their civillians are thrashed and beaten and tortured enough, they will ultimately lose their will to fight and surrender. Thirdly, it also effects the enemy's army: it can cause a great deal of fear and terror in the opponent's ranks because all of his troops are worried about their family, friends, and home.