The Scorching

While not a proper "Nuclear Apocalypse" humans generally expected, there was a glitch in some launch systems which caused a lot of destruction in 2045. Not many people know exactly what happened (M included), but it more or less destroyed Australia, some of England, and a lot of Northwestern United States. The radiation made most of those locations untouchable for a time until somewhat recently where enough of an advancement in technology helped them through it.

The radiation mended with the odd composition of the Red Fog, and created an orange-growth like substance which generated spores, making locales go moderately insane. Not zombie-style mind you, more of a "psychotically gang-forming murders" type. It wasn't permanent, as long as they were kept away from the substance for several hours straight.

Even through the insanity, the raiders found this out and purposefully carried around the orange substance, donning it on clothing and vehicles.

It took several years to eradicate it all, and there was a Druidic organization formed of metahumans with plant-forming or earth-altering abilities to help rejuvenate the land, but it all still has not recovered. This caused a debate against the Red Fog that M uses to block out the sun, however temporarily.

After a century or so, the Knights of Nahzreheim claimed some of the locations made unlivable by this tragedy, and created their own country.