I think war is always useless, money? Power? Do you need it to live happy?
Oh and nothing justifies this:
Depends on point of view
Point of view 1: Why war? Millions of people die. millions lost their's family, millions gets homeless. war shouldn't exist.
Point of view 2: War maybe is nescessary, but depends, after every war, example World War 2, even if people die, after it, tons of technologic evolutions happen.