This world is not a world as we know it. In fact, it is very different, and it is almost a dead world. This is how it all began.
In 1947, the transistor was not discovered and miniaturization of electronics was neglected. Sometime before 1969, in an attempt to mitigate the influence of Communism, the United States adopts a system of 13 Commonwealths. In 1970, China fails to adopt any free market reforms and remains similar to what it was under Mao. In 1991 the USSR did not collapse. No major international conflicts would take place until the middle of the twenty-first century. In 2052, the oil rich Middle East nations raised oil prices causing the economic collapse of many smaller nations. The European Commonwealth (analogous to the real world European Union), similarly dependent on oil imports from the Middle East, begins the Resource Wars by responding with military force. The United Nations, weakened by its inability to prevent the conflict, attempts to intervene. Many of its member nations respond by withdrawing and the UN disbands that year. The United States, being supplied by oil from Texas and Mexico, escaped any direct impact from the European conflicts. They were, however, to have their own problems. In 2052, the Texas oil fields were exhausted, making the Americans vulnerable to their own energy shortages. In 2053, the New Plague begins to ravage the US population, causing two-hundred thousand deaths and prompting the closure of her borders. Nuclear fears grip the country when, in the same year, Tel Aviv is destroyed by a terrorist nuclear weapon and, in the following year, warring nations exchanged nuclear weapons in the Middle East. In response, the Americans begin Project Safehouse: a series of underground Vaults designed to survive nuclear war or biological plague.
In 2059, oil resources become increasingly scarce. In order to secure the Alaskan oil fields, the United States ramps up its military presence in that state creating the Anchorage Front Line. Relations with Canada are strained as the Americans press to have their military units guard on Canadian soil to protect the Alaskan pipeline.
In 2060, the Middle East oil fields run dry. This not only ends the Resource Wars in Europe, but the European Commonwealth as well. Without a common enemy, the European nations begin fighting among each other for the remaining resources. Fossil fuels become too expensive to use in automobiles and alternatives begin to appear in the market. Advances in nuclear technology allow its use in automobile engines.
n 2066, the Resource Wars shift to the other side of the globe. China, her oil reserves exhausted and her economy near collapse, invades Alaska. America strongarms Canada into allowing troops and planes to move across Canadian territory on their way to the Alaskan theater. Relations between the neighboring countries would continue to worsen as the Americans help themselves to Canadian resources, ignoring Canadian protests. Many Americans begin referring to Canada as “Little America.” Their comments do not help the situation. In 2072, the Chinese-American war grinds on. While American power armor proves effective in localized conflicts, they are insufficient to completely dislodge the Chinese. US continues to demand more resources from Canada. When an attempt is made to sabotage the oil pipeline, the Americans (officially) begin to annex Canada. In 2076, the annexation is complete. Also that year Americans deploy the T-51b power armor to the Chinese mainland. The suits are highly effective and American troops cut a swath through Chinese territory.
In early 2077, the Americans reclaim Alaska but no armistice is signed. Those in positions to foresee the nuclear conflagration make final preparations: Robert House puts himself in stasis. The President and the Enclave retreat to the Poseidon oil rig. The American public, having been exposed to too many false alarms, largely ignore the warning sirens when the bombs begin to fall. Many Vaults are underpopulated as their doors are shut.
The collapse of global civilization made it impossible to ascertain the full extent of the damage wrought by the nuclear bombs. As viewed from orbit, there were clear signs of a global catastrophe: parts of Western Europe and the USSR received nuclear blasts. Asia and the Middle East were encased under the ice from the subsequent nuclear winter. Antarctica's ice sheet was blackened and much of the world's oceans were tinted green by radiation. The Great War's enduring legacy was the radiation that spread in its wake. Many of the plants and animals that survived the nuclear fire were killed by the irradiated rain that fell a week later. Of those that survived, many were mutated by 2080.
The American mainland was reduced to wasteland. Most major American cities, with a few exceptions such as Pittsburgh and Las Vegas, were razed by the bombs. Even the surviving cities were reduced to hellish ruin as society rapidly disintegrated.
The Vaults were never meant to save anybody.
[Courtesy Nukapedia, the unoffical Fallout Wiki.]