THIS IS YOUR POST-APOCALYPSE THREAT DOWN!
You might be aware of the threats that can cause complete collapse of society, but what are the main threats after society has collapsed? Here are the top 17 threats that will be present in any collapse of society. This does not include a continuation of any of the possible causes (e.g. nuclear winter, pandemic). I've listed them in order of least threatening to most threatening. Depending on your situation, your threats could be in a different order.
17) PACKS OF DOGS
Some dogs will get loose and survive. They will return to their primal instincts. They'll eat house cats and dead bodies. Not a major threat, but you might come across them. They could have rabies and parasites. They might go after your chickens and rabbits.
16) CITY FIRES
There won't be any firefighters around to put out fires. There will be explosions as people abandon their jobs and people will be using fire to cook and get warm. Fires are bound to start. Once they do, no one will put them out. I estimate 70% of cities will burn. These are also a low threat, because you should have bugged out before this happens. However, it will cause consequential threats as we will see below.
15) CHILLED TEMPERATURES
As a result of city fires and forest fires that will rage out of control with no one to put them out, we can expect a mild nuclear winter. The sun will be blocked out by all the smoke, so we will get chilled temperatures. This makes survival more harsh and grow seasons will shrink.
With lack of hygiene, lack of clean water, no vaccinations, no treatments, no mosquito abatement programs, diseases will surely be on the rise. We can certainly expect third-world type diseases to enter developed countries. In the US, malaria and West Nile Virus will spread. Sexual Transmitted Diseases will spread into certain communities. If you get sick, treatment will be hard to find. Your best advantage will be to stay isolated and drink clean water.
There will be plenty of common thieves. When there's not enough food to go around, people turn to a life of crime. If they find your camp, it could result in gunfights. If you're lucky, they will just steal and leave. If you're luckier, you can catch them and exact punishment. If you're luckier-er, you can catch them, utilize them for hard labor, and eventually they join your alliance (Remember, a lot of these people would have never stolen anything pre-collapse). If you're luckiest, you'll be in a position so hidden, that you never have to deal with thieves.
12) AIR POLLUTION (ASH)
As forests and cities burn, the air will be polluted with poisonous gases and tons of ash that will rain down for months in some locations. Try to bug out to a location that is not downwind of cities and forests. All this pollution will be bad for your lungs and cause sickness and induce asthma attacks for some people. PLUS, it will rain down on your crops. A layer of ash that falls onto leaves will prevent photosynthesis from happening. You might need to grow your plants under plastic or dust off your crops every morning around 9am.
11) APOSTATE MILITARY GROUPS
You've probably considered the possibility of gangs or warlords rising to power, but you should also consider this possibility too. I expect most military guys to abandon their posts or be dismissed by their superiors to go home and be with their loved ones. However, some of these guys will be on base thousands of miles from home and won't make it back. They will also be forward thinking and realize that it is going to get ugly quick. I believe there will be some good military groups, some bad military groups, and some in between military goups that band together and survive. Some examples of this have shown up in film (28 Days Later and Revolution on NBC). I think most of the military groups that survive will be good, but we can't eliminate the possibility of apostate military groups who use their superior weapons and training to rise to power. We love our military, but let's be honest, there are a lot of young guys in there who simply don't have the morals and values necessary. Hopefully, these apostate groups become rivals to the cartels and prison gangs.
10) HUMAN HORDES
Zombies everywhere! That's what they will be like when they evacuate cities as the water turns off and conditions deteriorate. I have love for my fellow man, but they will be like locusts looking for anything to eat. We would help them if we could, and we might be able to help some, but we can't help everybody. And obviously FEMA won't be able to do that. So, the natural result is that they are a threat. Your best bet is to try and avoid them, so you don't even have to deal with the pain and suffering.
As a result of the constant smoky skies, we will see a mild nuclear winter. Weather patterns and climates will change for a year or two. I think this will result in a temporary drought in many places. That's bad news for crops and possibly your anticipated water source.
If you are reading this, you are probably somewhat involved in the prepper movement. Still, s*%t happens to the best of us. Our food can be stolen. Our crops might fail. Animals will be hunted to the brink of extinction and bodies of water will be over-fished. There could be some unknown factor as well. Starvation is still a threat.
Our water ways and irrigation systems are very complex and require continual human control. Right now, our current levels of water flow require water being drawn out for human and agricultural use. When water is no longer drawn out for these purposes, we can assume that rivers, streams, lakes, deltas, and water tables will return to pre-human levels. Levees and damns won't be able to hold the excess water. Water breaching will happen in many different locations. Also, as the years pass, damns will begin to break and kill many people in flash floods. This is just another reason why the mountains are all the more attractive post-apocalypse. For additional help with this issue, take a look at the USGS 100 year flood maps, so you can see what areas are in danger.
6) STREET GANGS
They are currently a form of organized crime. Unlike the police, national guard, and military, who will largely disband and be with their families, gangs will likely coalesce and be strengthened. They will have the weapons and numbers. It will only take a week or two, before they begin systematically looting and stockpiling food. They will be deadly and dangerous.
5) FOREST FIRES
As spoken of already, these will happen. Most of them will be started accidentally by people who are learning to cook on open fire and warm themselves with fire. Yep, it's a brand new concept for some people. Not only will they cause all the atmospheric and crop problems, but they can cause direct problems. If you bug out to the forest, which is basically what I recommend, you might have to deal with forest fires. If the forest is your lifeline for foraging, hunting, and camouflage, it could be taken away from you. More startling is the fact that a forest fire can come upon you with very little warning. It might be 4am and all of a sudden there is increased wind and an orange glow outside. You might not have time to grab all your supplies. Be aware of all the bodies of water in every direction, but especially downwind and uphill of your current position, so that you can jump in and take cover in a worst case scenario.
4) PRISON GANGS
Similar to street gangs, but these guys are usually more violent and deadly. In a collapsed society, most likely these guys will be released or escape at the same time. They will be far from their loved ones, so most won't try to find their families. These guys will transform into raiding, looting, raping gangs in less than a day. Bug out to a location that is far from any prison. Heck, they might even make their former prison, their new HQ. It has great defenses after all.
3) NUCLEAR RADIATION AND FALLOUT
From the talk I've seen about nuclear power plants, it seems the consensus is that there is a real concern of nuclear power plants going into nuclear meltdown when society collapses. This will cause the contamination of water nearby and the wind will carry lethal radiation 100 miles downwind. With dozens of nuclear power plants in the US, nuclear radiation and fallout becomes a serious threat. Do not try to survive near a nuclear power plant or downwind of one. If nuclear radiation and fallout is a top threat without bombs being dropped, imagine how much of a threat it would be if there was a nuclear war.
Warlords and their militias will rise up. They could have a criminal background or not, but the main difference from these guys and other gangs is that the warlord will be an intelligent man who adapts and thrives in a post-apocalyptic world. They will also learn to be ruthless.
1) DRUG CARTELS
Public enemy #1 will be the drug cartels. These cartels are currently the largest illegitimate organization in North America. When the military, national guard, police, and border patrol dissolve, cartels will have nobody standing in their way. They will spill over the border like nobody's business. They will establish strongholds in LA, Phoenix, and San Antonio. They are already accustomed to savage crimes. They behead people in Mexico on a regular basis. In a post-apocalyptic world, drug cartels will be like kids in a candy store. They will have the numbers, the guns, the ruthless mentality, the intelligence, and the pre-established networks. They will roll over entire areas and become the first evil empires.