Initially covered in Common Horrors the Population Contraction was a massive depopulation event that surpassed the Black Death both in numbers and percentages in terms of loss of population.
Setting the Stage
By the zenith of the Petroleum Era, the world population had grown to somewhere between nine and ten billion people. The arcologies were being built to handle the rapidly growing population, as were a variety of green technologies to keep that many people fed. Famine and human suffering also remained fairly high as there were a number of regions that had populations that vastly outstretched the local resources to feed and support them, such as some serious hellholes in Saharan and Sub-Saharan Africa, SE Asia, and large sections of the Muslim World, but most prominently, Indonesia. This massive population is one of the key factors that pushed the Resource Wars to the level of escalation they reached. The Federal Superstates had massive appetites for cheap energy and goods, and had the military hardware and will to use it to ensure their low cost way of life. It is most often blamed on the United States of America but India, China, Russia, and the European Union were all also involved to one extent or another.
The wars erupted in South America and Africa, areas with the lowest level of resource exploitation and the largest amounts of remaining oil. Many people were killed in the Resource Wars but as a percentage of population, this number was relatively unimportant. It was also considered unimportant as most of the people killed were either African or South American.
Out with a whimper
The Resource Wars ended not on a hard preset date,but in a general sense that military operations ceased around most of the world. Tanks and aircraft required copious amounts of fuel as did the ships that supported them. The aircraft were grounded, and thousands of tanks and other hardware was abandoned as many factions sought to bring their troops home on the last trips of many non-nuclear ships. The high waste of the Petroleum Era was somewhat offset by Green Energy Initiatives, but these were simply not enough. By the end of the Petroleum Era there were approximately 135 nuclear reactors in North America, and more than half of them had previously been dedicated to maintaining internet servers, while as an example, one existed to pump water over the mountains to one city in California. This was simply not enough to light the homes of almost 600 million Americans. The situation was in many cases worse in other nations. Power rationing went into effect, internet curfews went into effect, but none of it could deal with the fact that an era had ended. This is all seen in hindsight, as during the post war collapse few nations were willing to accept what was coming. None had adequately prepared for it, not on the level that was required.
The lights went out, the internet went down, and the Second Dark Age had begun.
Let us Revive Ancient Hatreds and Let Slip the Dogs of War
Bloody massacres and riots quickly followed as foreign aid ended and famines went from bad to desparate. In some places, bad blood had been held in check by the threat of Global Peacekeeping forces, economic sanctions, and bribe like supplies of sundry goods. All of that was gone and in short order the gloves came off and violence erupted. Israel nuked Tehran and several other major Arab cities, and most of the Levant was watered with blood in a religious genocide between the better armed Jews and more numerous Muslims. Tribal violence, such as the sort that exploded in Rwanda boiled over again and again in Africa. China went through several rounds of crack downs and purges as the country started to break up. Riots were common across Europe and America. Racial violence between caucasians and hispanics was endemic across large portions of the disintegrating country.
By the end of a generation, the Federal Superstates were gone. There was simply no way for a modern superpower to exist in the Post-Petroleum age.
But in the background, a different threat had appeared. With cheap fuel gone, industrialized agriculture was butchered. Since the 1960s, global food production depended on machines working fields that were artificially fertilized and artificially irrigated. All this was done with petroleum or electricity. Phosphate mining for cheap fertilizer dried up, crop yields started falling dramatically, and soon large swaths of formerly productive farmland were fallow and being reclaimed by prairie grass and other steppe plants. Hunger was a common theme in the Second Dark Age. But mankind hadn't collectively forgotten everything from the last 12,000 years of civilization. Gardening went from ornamental to food production, and local produce became the only produce.
Some areas around the world saw some deplorable practices and conditions, local warlords reinstating slavery to man their fields. Other places saw a brief resurgence of feudalism, with the neo nobility being the ones who held alternate energy sources, such as hydroelectric dams, nuke plants, or being Navy admirals and such who could still command the loyalty of a nuke powered warship. The Arcologies remained, and with their high return recycling systems and self contained power supplies, remained as the embers of hope for a new age.
There are, however, dissenting opinions on the matter.
A Scared Old World
Without cheap food, cheap energy and cheap medicine, the world was a much darker and more serious place. Topical matters like television talent shows, social media and the like were blown away by concerns like food and self preservation. It was not the brave new world that parents wanted for their children. Across much of the globe it was a painfully uncertain future. Where there were 500 television channels, if there was one or two in an area it was a gift even if the shows were syndicated. Commercials were just salt in the wound, there weren't going to be new import autos next year, no one was going to play the sweet new computer game, and that hot movie coming to theatres soon came and went. Time to get back to trying to figure out how to get a horse to pull a plow.
People didn't have children.
The population went into decline, and this decline lasted for almost a century. The matter was compounded by the fact that infant mortality increased, so that of the decreasing number of infants being born, percentage wise, fewer were surviving. Formerly benign illnesses such as chicken pox and influenza returned to being killers, especially of the elderly and the young. In previous human eras, calamity and the collapse of nations did not have such an impact on the common populace. When Rome fell, farmers continued farming as they had before. After the fall of the Petroleum era, those folk who had access to alternative fuels continued farming with machines, albeit on a much smaller scale. Other places were forced to relearn millenia old farming techniques, often painfully so.
The Good Old Amish Way
Eventually the Contraction bottomed out, bringing the world population down to somewhere in the vicinity of 1.65 billion, or the world population of 1912. This left vast sections of the planet empty of human population. Then, the Second Renaissance started blooming. This spread would take another two generations before it was fully realized, but prepackaged food started being shipped out from the arcos, new arcos were being built, and the new nations started seriously forming by that point. Prior to that, there were regional governments, usually along the lines of city-states, and leagues of cities that shared their remaining resources, or pooled their common goods.
The lights started coming back on and the internet had gone through its second and third generations isolated in arco to arco networks, connected by satellites. The third generation started being phased out while the fourth generation Cognitive Network was being integrated to the system and was expanding. There was hope again, there was media entertainment, and tinned meat that didn't spoil, and then electric trucks starting showing up, doling out medications, food goods, and protection where it was needed.
People started having children again.
The Manpower Shortage
New nations had appeared, such as the Commonwealth of New England, as old nations had also restored themselves, such as Germany and South Africa. This created new demands for workers, new demands for soldiers, and there simply were not enough people to go around and do all the jobs that were needed.
The population contraction was over, and Population Augmentation Projects started. By the current date of the Cosmic Era, the population has grown to around 3 billion and is starting to show signs of leveling off rather than following it previous growth. By the time of the current era, there are still senior citizens around who remember the pre-Renaissance days, and there is a large amount of Dark Age literature that covers the trials and suffering of that bleak era, as well an almost conscience like cultural rejection of the ideals and moralities of the Petroleum Era.