3 being able to rebuild after an apocalypse is better then being ravaged by disease and hunger due to lack of resources to go around the 15 billion ppl of the world.
now that last one might be a bit confusing so let me explain (you can skip over this if you already understand)
first in a world that never had any war there would be far more people than there is today because no one ever killed them and we are at the top of the food chain so no animal kills us meaning 15 billion people and not the 6.5 billion today
next war has motivated millions (yes millions) of advances in every part of our lives with out it we would be looking at a far less developed world then our own
third with the 15 billion people in the world the amount of space available for agriculture among other things would be dwindled to nearly nothing so there would be less resources like food to go around to the 15 billion ppl
with that in mind there is already not enough food with what the world has now to feed everyone (although there might be if everyone shared [which by the way they don't]) so you take less food then right now and then split it up in 3 times smaller portions then today and you get starvation on a global scale
fourth with the lack of technology medicine would be even further less developed then today so the would would be further rampaged by disease
and this is just to name a few problems that comes up just because there was never war