I'd have to go with the semi-Biblical route.
All the nations of the world fight in an apocalyptic war and men turn into debased wretches, mere shadows of even their very flawed former selves! People will be killed and orgies will be held in the decaying corpses, blood, and excrement! The Devil Himself will take over the world and demons will burst forth from the ground feasting on the living! The sky will turn to fire and rain blood and and and LAVA!!!! SUCH IS THE PUNISHMENT OF THE WICKED AHAHAHAHAHAHAHAHAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA! You will fear every shadow, you will never slake your thirst with pure water or taste of tasty foods (yes that's right) ever a-fucking-gain! You will breathe FIRE! Your children will be taken from you, mankind will be enslaved as twisted amusement for horrifying beasts! Some kind of Gregorian chant will always be heard over your cries of torment because it happens in movies! Many of us, in all honesty, will be summarily sodomized with various objects. Sorry but it's true! That's how demons roll dawg! Meanwhile in Africa, demons fight crocodiles and gorrillas. Man that's a fucking epic duel right there. Satan will feast on endangered animals... MEANING EVERYTHING THAT BREATHES AWWW HAW HAW HAW!
Or something like that. Oh yeah there will be lightning too. Red lightning from clouds raining BLOOD AND AXES!!! (Ahhhh!)