I was once asked if I thought the socialist party was the best thing to happen to Germany? This was my response.
The socialist party was formed and backed by nations such as Britain and France and possibly the United States, Russia and Japan, they did this in accordance with Hitlers already rising popularity and his obsession with arian superiority, which was a minority and would create lots of space.
Mass unemployment, of which Germany was the hardest hit. War creates both industry and population reduction. The leaders of the world super powers backed the socialist party so that Adolf Hitler could enact the plan that would lead Germany and the rest of the world out of the great depression, WW2.
If humanity approaches it's boundaries again it will lead to mass unemployment, this will cause a global economic crisis. If this happens the leaders of the world superpowers will devise a plan to plunge humanity into WW3, they will do this because they realize it is now humanities only hope for survival.
Unfortunately when you open pandoras box it releases all of the evils of mankind, leaving only hope inside, it very well could unleash armaggeddon. The guns those armies hold are massive, they could bring a fire that would scorch the entire earth.