Before the disease hits
Even though the world became a much worse place after the shit hit the fan it was no paradise before. Even though the evidence had been there people had decided putting their hands in the sand was the better option, so nothing was done to counteract the climate changes occurring all over the planet. This made the political environment even more unstable as the effects of the climate changes reared its ugly head.
The weather was changing, everything became more extreme. The droughts became drier and longer, with famines following in the poorer part of the world. Water had always been a source of conflict, and as it became more of a scarcity in some places tension grew high. Who had ownership of the water in a river became the big question of the day, and everyone figured it was them. And when nobody backed down the long predicted water wars erupted, bring great devastation.
But it wasn't only the warmth and shortage of water that became a problem. Storms seemed to be getting worse every year, bringing destruction and death in its path. Florida and the Caribbean was almost torn apart by a series of hurricanes the summer before the disease hit, and it was not an isolated case. Big storms hit everywhere it seemed.
Not only did the warm summers make it harder to grow decent crops, but the winters had become colder and longer. Now the growing season was shorter, and produced less, and there was growing concern that famine wouldn't be a third world problem exclusively for long.
The disease hits
Nobody knew where the disease came from, having laid dormant under the ice caps of the South Pole its origin remained a mystery. Its effects however did not remain a mystery.
At first nobody even noticed the disease. Due to its long incubation period and effective way of spreading itself through the air it had spread all over the world before anyone had even noticed. So when it hit, it hit hard. It was like something had triggered it into entering its next phase, as it erupted all over the planet almost simultaneously. Naturally, panic set in. Not only because of the sheer volume of people dying, or that loads of important people was infected as well, but mostly due to the disease making people into what could be described as zombies.
The disease was eating away at both the flesh and the mind of its host. The victims appearance would remind you a bit of leprosy or zombies, and their behavior soon turned from trippy or unfocused into something more menacing. They would become aggressive and whatever morality they once had held would be gone, they would be like wild animals attacking anything they saw. Luckily they would die after a while, not wander the Earth like zombies forever, but until they died they were a big menace to everyone.
Society crumbles
As many people were infected society soon started to crumble. The government in the United States tried to keep things under control, but when most of the government became ill the government soon collapsed. With both the president and vice-president running around the streets of Washington in rage, and being joined by most of the Senate, the military had no choice but to move in and take control.
However, at this point the breakdown of human technology had started as well. Communication infrastructure was soon to be a thing of the past, although some remnants of it would be usable for some time, but for the common man the only was of giving a message to someone in another town was to walk there themselves or pay someone to do it. This led to isolation which further fueled the paranoia among many.
Another problem was nuclear power plants melting down, shooting its radioactive load into the atmosphere. This was bad news as the radioactivity would make the disease mutate in more way than one.
Under military control
The military ruled with an iron fist. Marshall Law was introduced, and everyone having any symptoms resembling the disease was killed at sight. Either by the military or by mob that would form fast. Fear ruled the world.
Research on the disease was pitiful, and the military was instead trying to wipe out the disease by killing everyone who might be carrying it. This didn't work, so desperation grew among the generals. Soon the military was loosing control over the big cities, and withdrew back to military bases all over the country, with the main base being in Cheyenne Mountain.
Seeing as the big cities was overrun the military was getting desperate, and a desperate plan was put into action. Nuclear bombs over the big cities. The big cities on the east coast was nuked, and laid to nuclear wastelands. New York City, Philadelphia, Washington. All gone, and more cities with them. It didn't work though, and the military disbanded its plans to nuke the big cities in California. Having already evacuated the cities they were mostly left to the infected, and those who either stayed behind or were left behind.
At the moment the military holds their ground in their bases, ruling the area around them with an iron fist. The military government resides in Cheyenne Mountain, desperate to regain control over the country.
The disease after the first generation
When the non-infected got fewer and fewer the disease had a harder time to spread, so the nuclear waste was just what it needed to speed up the mutating. From having spread through the air it now found new ways of spreading, like through the meat of animals acting like carriers. With a shortage of food people wasn't picky with what animals they ate, and this helped spreading the disease. Not all animals was carriers though, and people wasn't aware that some were carriers either.
However, not everyone was affected by the disease in the same way. Some diseases would provide partial immunity against the plague, and others would make you more vulnerable. There were even those managing to fight off the disease. The big question was if they would be immune now? And if so, would they be immune towards all of the different mutations, or just the one they had fought off?
The situation at present
With the government having lost control the situation is grim. Some communities manage to function somewhat, especially in those pockets that wasn't hit hard by the disease or the nuclear fallout. However, the general rule is that the strong will survive and the weak will perish. There are gangs roaming the country, some are deserters from the army, taking what they want and who they want. The times are not safe.
The disease is the boogeyman. When someone thinks the disease might be around panic sets in, and people are killed. All kinds of methods are being used to try and avoid the disease, like boiling all the water.