As long as men and women are bored, war provides an opportunity for adventure, this bored people will enlist to fight for their countries.
As long power is pleasurable, and war offers an opportunity to get power, there will be war.
Men and women are not rational actors. If we were, we would pursue peace.
As long as countries each have their own army, there will be aggression. So we must hope for peace at all times but prepare for war, because, as I have said it is inevitable. And make no mistake, I am a pacifist, consider being in the army equally as stupid as believing in original sin or Mohammed going to heaven on a Pegasus.
Is there anything to be done to avoid war? Yes? People should be engaged in work that has opportunity for adventure. Boring work schedule leads to ennui and with it, any opportunity to join in a war would be quite tempting for a big majority.