In March of 1998, a Great Thermonuclear War occurred that nearly brought humanity to extinction. As the war is never referred to with any specific name, The War can be a reasonable designation for the conflict.
There are, however, alternate names that can be used. By 2048, Floridians often referred to the war as The Change. World War III could also be a name as it is generally used to refer to nuclear conflict. The Holocaust has been used by Gramps Astor as well.
The War has its roots in the Cold War, a long tension between the United States and the Soviet Union beginning directly after World War II. Both parties possessed vast arsenals of nuclear weapons, but neither country would commence nuclear warfare out of fear of Mutually Assured Destruction. Thus, a long uneasiness permeated throughout the world.
In 1983, the United States commenced construction on the Citadel Starstation. The Soviet Union claimed that it was merely a military launching platform, alarming several nonaligned nations.
The Drug Wars (1987-1993) worsened the already high tensions between the United States and the Soviet Union. It seems that previous conflicts led up to this, as America was seeking to create allies perhaps in preparation for a more massive war. Many of the underdeveloped, poverty-stricken countries of South America were conquered and their legislative bodies replaced with puppet governments fiercly loyal to the United States.
The Soviet Union did not fall in 1991 as it did in our world, thus continuing the Cold War well into the 1990s.
In March of 1998, the AI of Sleeper Base Two sent a fake signal about an imminent Soviet nuclear attack. The world went to DEFCON 1, and all nuclear-capable nations launched everything they had. This resulted in the near extinction of humanity. The global communications network was disrupted and the Citadel Starstation was destroyed in the process.
It is unknown exactly how many cities or which cities were hit with ICBMs, but a small few are known. Los Angeles, California appears to have been hit hard by nuclear weaponry, and the immense radiation west of Darwin suggests that Phoenix, Arizona must have been completely destroyed. Soviet missiles managed to miss the city of Las Vegas, Nevada completely, despite apparent attempts to level it to the ground. Atlanta, Georgia and several military installations nearby were hit directly. Apparently these strikes were so severe they triggered a seismic backlash that caused the dislodging of Florida from the mainland United States. Central Florida was hit with neutron and chemical weapons because of the presence of Cape Canaveral, which America's enemies wished to preserve for their own use.
The War ultimately destroyed the Earth and left the once highly numbered humans in low millions. As mentioned above, the nuclear strikes on Georgia were so severe that they triggered a seismic backlash that caused the dislodging of Florida from the mainland United States. This divide between Florida and the mainland was 5 miles across, and no one dared to make the journey. In the weeks following the war, many Floridians attempted to re-establish communications with the mainland, but were met with silence.
The fallout killed many of the survivors, and apparently drove some mad as well. The radiation caused wild mutations, some of which include the Desert Dwellers, Night Terrors and even large, vicious worms. The chemical weapons used in Florida produced similar mutations, such as the Mute Widows.
The War appears to have caused the melting of the polar ice caps, which has caused major flooding in certain areas. For instance, the Gulf of California seems to have eroded to the North.
The oceans are apparently filled with large, mutated sea creatures, and thus cannot be traveled through.