1983: Doomsday
Idea from the Alternate History Wiki Article, all credits go to the creator of the Article
It all begins on September 19th, 1983, on which a seemingly unimportant decision to send an ambitious Colonel of the USSR to a training seminar (taking the place of an ill-plagued colleague), has global implications.
This decision leads to a different outcome of a well-known, though often underestimated, event that took place on September 26, 1983.
In our timeline, Colonel Stanislav Petrov was the watch officer on duty that day at the Serpukhov-15 bunker near Moscow, monitoring for a US missile attack on the Soviet Union.
Suddenly, the computer-based warning systems reported several US nuclear missiles approaching Soviet territory. In our timeline, Colonel Petrov believed the information to be false and did not alert the Kremlin to the data he was receiving. Given Cold War tensions at the time, such information would likely have convinced the Soviets that the US had launched a first strike in an attempt to "cut off the head," and they would have been forced to launch their nuclear weapons in the false belief that it was a counterstrike.
Consequently, since in our timeline the world now knows about this event, it is now often considered to have been the moment closest to a nuclear war between the USSR and the USA during the Cold War. Colonel Petrov has been honored as one of the few true "world saviors," and several investigations have proven the seriousness of this event.
This timeline postulates the results after Colonel Petrov was sent to another installation before September 26th, 1983. The officer now on duty on September 26th considers the alert to be accurate and immediately contacts his superiors. Within minutes, the leaders decide to launch the whole Soviet nuclear arsenal. Logically, the Americans react by launching as well. By the time the first alerted missile is proven to be a false alarm, it is too late. Thousands of nuclear warheads subsequently detonate over targets worldwide. Surprisingly, the People's Republic of China was attacked by Soviet nuclear missiles as well, and part of their arsenal is launched in response at the USSR.
The results of this total nuclear exchange are close to the forecasts of almost complete worldwide destruction and the "nuclear holocaust" as predicted by many scientists of this time. This results in as many as a billion people killed initially, and another billion in the subsequent environmental disaster that followed shortly thereafter.
With the world largely devastated, and most of the Northern and parts of the Southern Hemisphere in ruins, the estimated 800 million survivors in these areas desperately try to keep together what is left of human society. They are facing challenges that are seemingly impossible.
After an incredibly horrifying first few years post-Doomsday, a handful of regions, territories, and countries stabilize and master basic problems such as food and medical supplies. As time passes and the recovery continues, new (sometimes surprising) alliances are formed. A new, fragile world order emerges from the ashes. Initial hopes of some survivors for a united mankind (or at least warfare and destruction being ended forever) quickly prove false. Indeed, the world is light-years away from any Utopian imaginations. Famine, disease, and lack of resources provoke conflicts and wars in large parts of the world, thus devastating all the carefully achieved recovery.
Now, 30 years after the devastating "Doomsday" brought mankind to the edge of total extinction, a few moving moments have spread the hope for a more peaceful future for mankind, such as the foundation of the new "League of Nations" September 26th, 2008.
Basically humanity has survived a Nuclear Holocaust and they have begun to rebuild. The year is 2016 and nothing is like what it should be. Technology is 20 to 30 years less advanced than it is in our timeline, meaning that we do not have advanced drones like we do now, but we still have easy contact with other nations. Early satellites have once again been launched into outer space.
Depending on how this goes I add the Nation Sheet.