Mankind has been pleagued by wars, it cannot get away from it. We fight amongst ourselves for wealth, power, land, and supperiority. When mankind discovered space people thought that would change, boy were they wrong. Mankind brought it to the next level.
No longer did we fight over land by the mile, we fought across the universe by the light year. Millions died as the wars broke out one after another, whole star systems abandoned due to the amount of wrecks. Mankind realized after the creation of the doomsday device, that things needed to change. A weapon that could be used to destroy even the mightiest of ships, a weapon that could break through even the strongest walls.
So what changed? Nothing, so long as mankind exists, so will greed, and with that so will warfare. The only things that have changed is the weapons and the ships they use, now more powerful. They used to say god save the queen, now I say god save mankind.