6) Nuclear War

A very realistic fear that has plagued the darkest depths of mankind since the Cold War is the thought of a nuclear war. As of today, most major powers possess nuclear arms capable of eradicating several thousands of human lives at the press of a button, but doing so would consequentially lead to revenge spun retaliation and the beginning of a nuclear holocaust.  

Being able to cover a mushroom cloud with your thumb indicates a safe distance from the impact zone

While the possibility of a nuclear war is very real the aspect of one occurring is slim as there is not a need for such exceedingly powerful weapons is not required in this day and time. This is not to say that something could not occur to set offer a nuclear war as this does seem to grow more and more possible as bonds between nations dwindle and the desire for power among countries grow.

Despite the reasoning for a nation to rely on nuclear warfare as a means of assaulting another nation it would more than likely be met with counter strike that would lead to WWIII and a post-apocalyptic nuclear wasteland that very few people would be able to survive. Such a premise has been imagined in the Fallout Series, however, I feel as though the sickening reality of a nuclear based apocalypse would be much grimmer then the bottle cap currency style gameplay of fallout.

The radioactive aftermath of a nuclear bomb will leave the entire area incapable of supporting life

Barron nuclear waste lined soil too corroded to ever be used for growing food or living on for generations to come. Black smudged stained shadows left as a reference to what had been standing there sheer moments before the war. Those who managed to survive would be less than human, but not quite animal either. They would just be some form of humanoid beings who managed not to die from the third world war.