Simplistically speaking,

It takes a soldier to fire the gun.
To make it, you need a working man.
To feed him, the farmer will plow the land
- it all goes hand in hand.
But to feed the soldier, and the man
who makes the gun, you need more land;
and to get more land, of course, you need a soldier.

We're in a spiral, folks. To break out of it it takes serious sacrifice, like whole countries disbanding armies and trusting their neighbours. I'd love for that to happen, but I can't see it happening. Can you? So we remain in the spiral.