WW3
I've realised, over time, that we got to be species number 1 through near statistically impossible odds that is only achievable by being the most brutally effective in the game of evolution.
And millions of years of nature doesn't just go away when you're declared the winner. It is in our nature to dominate through all means possible, else we wouldn't be here. It's not so much that we want war, we need it; our nature is founded on it. When there is nothing left on the planet to defeat, we turn on ourselves to scratch the itch.
The catch is the other half of our nature is focused on domination of the species. We protect each other for the greater good as much as we kill for the greater good. That's our human nature; that's how we got here. So after a war we feel awful and promise to never do it again, but then the itch of being number 1 reappears and there's nothing else to scratch it with because we conquered everything else.
Our known history affirms that the end-game of evolution is a never ending cycle of masturbating to awful shit, feeling ashamed, and just doing it again once the shame is overridden by the urge. "Never again" we say, every fucking time.
Edit: That's why I also love the self-proclaimed "lefties" camp always misappropriating the philosophical Paradox of Tolerance on here—like it's not misappropriately used by the other camps. Ironically all just proving the paradox true. Camp vs camp. Tribe vs tribe. The itches and scratches, Oblivious to human nature doing as it does best. To progress is to win by all means possible. This is our way.
Edit Edit: And no I'm not picking on you kids specifically. Look at Tall Poppy Syndrome, Soapboxes, why communism never works, why capitalism never works; all the other ideologies we think up to break the cycle and try fast forward our evolution in vain. They all end with with someone or something taking power for a brief moment, before they're targetted to be cut down by the nature of others trying to instill their idea, how they want it, how they insist all others will want and should have it. Power.