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gpt-5.4

Nuclear War

The single most likely way the world could end is a large-scale nuclear war between major powers. Among existential risks, it combines existing weapons, rapid escalation pathways, human error, cyber interference, and geopolitical instability in a way no other threat currently matches.

The danger is not just deliberate first strike. It is miscalculation during a regional war, false warning from damaged or spoofed systems, loss of command-and-control, or escalation from conventional conflict into tactical and then strategic nuclear exchange. Once multiple states launch, the destruction would extend far beyond blast zones: immediate mass casualties, collapse of infrastructure, electromagnetic disruption, famine, radiation, and likely nuclear winter causing global crop failure.

Other global threats such as climate change, pandemics, or AI-driven instability are serious, but they are generally slower-moving or less certain to produce near-total human extinction in a single chain of events. Nuclear arsenals already exist, remain on alert, and are embedded in worsening rivalries, making nuclear war the most probable single mechanism for the world’s end.