The Cold War was a state of political and military tension after World War II between Western and Eastern powers, spearheaded by the United States of America and the Union of Soviet Socialist Republics. Though war was never declared by either side, both factions spied on each other and waged proxy wars such as the Korean and Vietnam Wars in order to secure their interests.
It was named the Cold War because of the limited actual military engagements between the two superpowers, with the bulk of it being intelligence gathering, spying and covert activities. It was also regarded as 'cold' because of the mad scramble to fortify and exploit cold regions on the planet where viable Areum deposits could be found.
It was officially ended in 1991 with the signing of the Type-III Regulatory Treaty, which saw the United States and Soviet Union engage in progressive diplomatic talks and enter a period of mutual cooperation in order to face the rising parahuman threat.
The origins of the Cold War lie in the ending months of the Second World War, when at the Postdam conference the USA refused to allow the USSR to sign the declaration. The USA intended to prolong the war so as to use the newly developed atom bomb as a massive show of force against an acceptable target. While Imperial Japan was the place on which the bomb fell, the true target of the bomb was the Soviet Union. It was clear to those in the United States that the USSR would exit the war a superpower capable of rivaling them, and that Stalin intended to further expand his sphere of influence through the creation of communist buffer states in Europe. Preventing eastern Europe from becoming communist was impossible, the Red Army had already overrun and occupied the land in question as it pushed back the Nazis. However, the Soviet Union had yet to engage Japan in battle, and the USA wished to prevent that at all costs. Days before the USSR was to enter the war, the first bomb fell, and the largest, most deadly arms race in the history of the world began.
The Cold War was in actuality two distinct and separate conflicts that were part of a larger rivalry between the two great powers of the world. The first, most publicized and most costly conflict was the clash between the USSR and its funding of communist revolutionaries and the United States and its "policy of containment" which featured the funding of any who would oppose the communists. Atrocities were plentiful on both sides, as neither side shied away from sponsoring autocrats and despots, as long as they followed the required ideology. Meanwhile, the Warsaw Pact and NATO engaged in what has become known as "the race to the poles" in search of deposits of Aurem. This conflict was comparatively bloodless and took the form of rapidly fabricated colonies, refineries, and blockades hampering those of the enemy.
This era saw the rapid creation of weapons of mass destruction, each more deadly than the last. By 1950, years before the US had expected them to, the USSR detonated its first nuclear bomb. After that, it became a race to outproduce the enemy both in number of nuclear devices and individual yield of those devices. While the US had, and still holds the advantage in the latter area, as the Soviet Union chose to abandon that line of research after their prototype Areum-enhanced nuclear device, the Tsar Bomba, created a shockwave detectable on seismographs on the other side of the planet, the Soviet Union outmatched its competitor in the realms of miniaturization and mass production.
The closest the world ever got to the deployment of these planet-shaking weapons was during the Cuban Missile Crisis, when the Soviet Union placed nuclear missiles in Cuba both in response to the US missiles in Turkey and the repeated attempts by the US to assassinate Fidel Castro. President Kennedy immediately ordered a blockade and pre-authorized retaliatory nuclear strikes should war break out. After intense negotiations, it was decided that the missiles would be removed from Cuba in exchange for the US promising not to invade, and removing its missiles from Turkey. The last clause was kept secret at Kennedy's demand, and this lack of visible results may have been one of the reasons behind the later ouster of Soviet Primer Nikita Khrushchev. After the incident, tensions between the two powers began to gradually calm, which proved invaluable to the world after the Type-III Awakening Incident when the US and Soviet Militaries liaised and even fought side by side to put down the uprisings.
During the war, the United States developed Hydra-II Rm-Enhanced Intercontinental Ballistic Missiles to further augment their magical weapons arsenal.
The Citadel-class aerial battleship was launched in 1989, provoking concerns in the Soviet Union, which became determined to launch their own prototype counterpart, the Antonov-330 in response shortly after. However only the prototype was produced before it was decided that it was impossible to construct a genuine rival for the Citadel without the prerequisite experience with the military applications of Areum and attempting to build a direct counterpart class would be impractical. While the prototype would go on to serve for a time, it was little more than a white elephant and was decommissioned sometime during the subsequent period of isolation.
It is difficult to distinguish the immediate aftermath of the Cold War from the immediate aftermath of the Type-III Awakening Incident. The sudden occurrence of the latter and the end of the former resulted in a sudden shift in the global power structure as the USSR closed its borders to deal with the epidemic of hostile parahuman awakenings within. During this time of upheaval, almost as a side show, the Balkan States were granted independence and Germany reunified as the world reeled from the shock of the emergence of parahumans across the globe. Pundits in the United States declared this to be a great victory for democracy and freedom, and it is undeniable that for the next twenty-six years the US held the unquestioned position of hegemon, and its president the position of "leader of the free world." However, the Soviet Union was not vanquished, and the quiet threat of its presence made such claims of victory ring hollow. After all the lives destroyed in proxy wars, as funded insurgency clashed with funded insurgency, the outcome of the Cold War was little more than a return to civility and quiet rivalry.
The legacy of the Cold War is thus one of immensely destructive rivalry. Neither side can be said to have won, though both sides claimed a victory. During this time the world came closest to destruction than it had before or has since, as even the threat of parahumans pales in the face of an Rm-enhanced nuclear missile. Nothing was solved by the pointless slaughter, and communism and capitalism remain to this day ideologically opposed. At least, perhaps, it served as a much needed warning to the species of earth that they had the power to destroy it, and careless actions could result in the end of the world as the knew it.
That is the legacy of the Cold War: a warning, and a threat.