World War III

The world of 2033 lies in ruins as a result of World War III (a.k.a. the Great War of 2013 or simply Armageddon). The great war is an integral part of the Metro Series canon, as it's the major event that predates the events of both the books and the games.

The event that has led to the post-nuclear reality of Metro 2033 has different names that vary between locations and from one source to another. It is commonly regarded as World War III, the Third World War, or the Great War of 2013 - as it's considered to be the last global conflict in human history to be on the same or greater scale than the first two preceding World Wars (it is worth noting that the First World War used to be known as The Great War, since it was the largest conflict thus far seen by mankind and was perceived as the "war to end all wars").

In novels from the Universe of Metro 2033 series we see the name of this conflict varies from place to place. The inhabitants of Kraków tend to call it the Conflagration due to widespread destruction wrought by the fires as a result of nuclear detonations. In Serdobsk, the event has been dubbed as the Beginning because it sparked a new era for humanity and planet Earth. However, Varsovians, as well as survivors elsewhere in Poland and Russia, usually refer to the war as Armageddon due to the obvious biblical reference. Alternatively, many people call it simply the Attack or the Catastrophe.

Overview
Very little is known about the war itself, including why and exactly how it was fought, though a promotional animation for Metro Last Light's site, "Enter the Metro" revealed that a total of 20,000 warheads were used and that the war began with a limited exchange between two Middle Eastern countries - appearing to be Iran or Iraq, and Lebanon or Israel. After the initial exchange, other nuclear-armed nations began their response; the end result was a massive global exchange of nuclear weaponry over a brief span of time.

While (at the time of writing) modern countries that are known to have nuclear weapons include France, Britain, China, North Korea, Israel, India, and Pakistan, it's implied in Metro 2034 that the United States was a definitive enemy of Russia during the Great War. In Metro 2035, a key spokesperson from Polis reveals that 140,000,000 or 139,000,000 Russians died during the war - which would mean that only 6 or 7 million endured, but it is uncertain how many of them survived the 20 years of post-apocalyptic conditions that followed.

What is certain, from Stepan's account of the war along with flashbacks and dialogue in Metro: Last Light, and the live-action shorts, nuclear weapons landed on Russian soil shortly before they responded. Several missiles were launched from launch sites across Russia only seconds before a nuclear bomb detonated over Moscow. After the exchange, Russian nuclear submarines enacted the Dead Hand contingency, and the majority launched their payload in retaliation, or stood down because of moral concerns or lack of new targets. Regardless, the entire world was completely devastated.

Post-exchange conditions
In the days following the nuclear exchange, the planet was transformed into a toxic dust bowl. Massive amounts of irradiated material began circulating around the globe, spreading throughout the atmosphere and blocking out the sun; the result was nuclear winter. The inability of plant life to maintain photosynthesis, coupled with severe radiation lead to the destabilization of the food chain, and the extinction or mutation of most animal life on the surface. These changes in the Earth's biosphere lead to the surface air being unsuitable for human life. 20 years after the war, many areas (especially in cities) are still irradiated, some so severely that only a few minutes' exposure is lethal. It's speculated that several billion people survived the initial exchange, but given the surface conditions, most died shortly after due to radiation exposure or starvation, or have become Dark Ones and humanimals.

Remnants of Humanity
The fate of the rest of the planet is unknown after the exchange. While the southern hemisphere of the globe was largely untouched by warheads, the infrastructure of every major nation was presumably devastated, making the damage impossible to repair and leading to the collapse of all global superpowers. It's assumed that, where possible, civilian populations did the same as the Russians and hid underground.

In Metro 2035, Artyom meets a group of survivors claiming to be from Murom in Russia, though the Rangers of the Order believe they are NATO spies. Artyom also hears radio broadcasts from the following places:
 * Saint Petersburg, Russia
 * Vladivostok, Russia
 * Kazan, Russia
 * Ufa, Russia
 * Mirny (either a Russian outpost in Antarctica or a town in Russia)
 * Sverdlovsk, Russia
 * Berlin, Germany
 * Paris, France
 * An unnamed English-speaking location

In Metro Exodus, Artyom hears radio broadcasts from the following countries: Argentina, Australia, Azerbaijan, Brazil, Canada, Central African Republic, Finland, France, Germany, Indonesia, Iran, Iraq, Italy, Japan, Norway, New Zealand, Poland, Slovenia, Croatia, South Africa, the United Kingdom, the United States, as well as other parts of Russia. This reveals that humanity continues to exist all over the world in civilised pockets. It basically confirms the information that had already been made canon earlier by the Universe of Metro 2033 extended book series.

A repeating official radio broadcast that Artyom picks up on the Aurora, likely dated to shortly after the bombs were dropped all over the world, warns the residents of the Russian Federation (or what remains of it) to stay away from the following cities due to dangerously high levels of radiation: Barnaul, Biysk, Kemerovo, Novokuznetsk, Novosibirsk, and Tomsk. Some citizens actually survived in the Novosibirsk Metro, but political instability and supply shortages led to internal turmoil that ultimately killed off almost everyone who was left.

Eurasia

 * The novel Piter reveals that inhabitants of St. Petersburg survived the nuclear war by hiding underground in the metro tunnels of their own city.
 * The story of The Roots of Heaven shows how once powerful organisations like the Roman Catholic Church turned into weak remnants, shadows of their former selves, but still continue to vie for influence over the faiths of Rome's few survivors.
 * Murancha and Heritage of the Ancestors tell us of the fates of survivors in other parts of the Russian Federation.
 * The Promised District and Whispers of the Fallen reveal that some numbers of people have also endured the nuclear holocaust in other parts of Eastern Europe - namely Poland and Ukraine.
 * Even more Polish locations are revealed to be inhabited by communities of survivors in The Abyss, The Tower, Achromatopsia, and other books. Some of the major cities that are known to have at least some human remnants are: Warsaw, Kraków, Wrocław, Gdańsk, Gdynia, Szczecin, Częstochowa, and Łódź.
 * Echo of an Extinguished World shows us that very small numbers of people have survived in the Dunmore caves of Ireland and within the Stockholm metro of Sweden.

The Americas

 * Heritage of the Ancestors hints at the possibility of survivors in Chile and perhaps other parts of South America.
 * In the collection of short stories titled In Ruins, we learn of people that persevered in Chicago.
 * The Outpost reveals that, much like elsewhere in the world, North America is mostly desolate and irradiated. What remains of humanity in the US is concentrated mostly in or around the "Outposts", heavily fortified and walled-off communities of survivors.
 * The same graphic novel also tells of some human survivors in parts of Canada.

Rest of World
On battlefields across the globe, groups of soldiers survived by hiding in their tanks. Many of these groups banded together into camps and tried to acquire radio contact with the remains of civilisation. In Towards the Light, it's revealed that some areas of the earth were not directly hit by any of the bombs. Locations such as Australia and most of South America were likely spared since they had no nuclear weapons to begin with. As shown in Metro 2035, areas on the surface not directly struck by the bombs remain fairly habitable, and it's likely the regions of the world spared from bombing are free from severe radiation or mutants. These regions, however, are most likely preoccupied with managing their own respective countries and uninterested in exploring the "destroyed" areas of the world at the time being. It can be assumed that the major leaders of participating countries at the time of the exchange enacted their respective Continuity of Government (with the exception of Russia in the video game canon), and are still alive and in power - although, given the state of their former nations, this matters little.

Metro Live Action Short
On the 24th of May 2012, a live action movie was posted to YouTube in promotion of Metro: Last Light. The film gave a snapshot of the moments before the bombs fell.

Metro Exodus
"Because the war is still going on! And you behave like fucking kids!"

- Stroin to Artyom and Anna

In Metro Exodus, it is rumored that World War 3 still rages on across the globe and never actually ended. According to Miller, after the nuclear attacks on Russia, the government chose to "play dead" to make the US and NATO forces think that the Russian military had been destroyed so there will be no more bombings on Russian soil. In order for the ruse to play out, the Moscow Defense Command constructed multiple radio jamming stations surrounding Moscow and the suburbs to blind their enemies.

It's later revealed that there are no occupation forces within Russia, and that the government was unable to enact their contingency plan, with a (presumably) Russian Army Officer revealing at gunpoint that once they arrived, there were no rations, before being executed by Colonel Miller.

Trivia

 * Comments made by the currency exchange booth survivor suggests that the war (or at least the first attack on Moscow) took place in early July 2013 - being sometime around July 5th. A diary entry in Metro Exodus puts the war's beginning as July 6th, 2013.
 * In the Metro 2033 novel, it states that a biological weapon was launched at the Kremlin and which went undetected by the Russian missile defense system. This explains why D6 was unoccupied as the occupants of the Kremlin were mostly killed in the biological attack and were not evacuated to D6 in time. The bio-weapon strike on the Kremlin is also mentioned in one of Artyom's journal notes in the Red Square mission of Metro: Last Light, which explains that the Kremlin was not nuked, but was instead hit by something "experimental" that "ate everything organic within a radius of a few miles".
 * Siberia, the Mid-Western United States, and much of the Southern hemisphere seems to have been spared from the atomic exchange, meaning that parts of the world could very well be better off than the rest due to not having been affected by the nuclear winter or heightened radiation levels quite as heavily. Furthermore, a comment made by a Ranger in D6 speculates that the Russian Government was moved to Siberia, most likely at the government bunkers under the Mount Yamantau, meaning that the destruction might not be as widespread as believed. Likewise, the American government could have been moved to the Cheyenne Mountain Complex in Colorado. While Metro Exodus disproves the theory that the government survived in Yamantau, the fate of the Cheyenne Mountain Complex remains unknown.
 * In Sam's Story, it's revealed that the city of Vladivostok was not directly hit with a nuclear strike, instead several missiles struck in a line off the coast, sending a man made tsunami to destroy the city.
 * In Metro 2034, it states that America developed an "anti-rocket system" meaning that some areas of America may have survived a nuclear strike.
 * Due to Moscow's own missile defense system (the A-135 anti-ballistic missile system), some areas of Moscow were speculated to not have been destroyed by the nuclear strikes. In Metro 2035, it's confirmed that most of Moscow survived the war physically intact, thanks to this defense system which targeted the nuclear weaponry in the sky before it could hit the city, but the destruction of the missiles caused a shower of radioactive shrapnel to fall across the city, leaving it uninhabitable.
 * In real life, the United States does operate a anti-ICBM system called GMD. Russia's equivalent anti-ICBM system would be the A-135.
 * It's unlikely for much conventional warfare to have taken place during or after the nuclear bombardment. Given that Flight 76715 was taken down by an electromagnetic pulse, it's reasonable to assume that most (if not all) conventional land forces were crippled straight away.