As the saying goes,
War is diplomacy conducted through other means. As much as it'd be nice to say there ain't-a going to be war no more, it's probably with us as long as conflict exists, as war is the ultimate means of resolving a conflict - this is not just its redeeming feature, it is why there is war. (As any attempt to reduce conflict by making everyone agree will automatically generate
yet more conflict by those who don't want to, the deck is stacked against you from the start, even so.)
That's not to say war can't be perfected. I find the oxymoronic concept of a "humane war" where the only ones killed are the soldiers who signed up to be one worth going towards. Or even a "virtual war" where two parties engage in a fair competition and abide by the results in lieu of actual combat. But, alas, until you can get everyone to agree on this (and we've already noted the futility of THAT) the old standby of mass slaughter is going to be with us in some capacity.