Nuclear War

The single most likely way the world could end is a large-scale nuclear war, most plausibly triggered by a major-power confrontation that escalates through miscalculation, cyber interference, false warning, or loss of command-and-control during a fast-moving crisis.

This stands out over other global threats because it combines existing weapons, short decision times, fragile deterrence, geopolitical rivalry, and civilization-ending destructive power. The world already has the means to do it; no scientific breakthrough is required. Tensions among nuclear-armed states remain high, arms-control systems are weaker than in past decades, autonomous and cyber systems increase uncertainty, and leaders in a crisis may act under minutes of pressure.

A full nuclear exchange could kill hundreds of millions directly, collapse food systems through nuclear winter, destroy infrastructure, trigger famine and disease worldwide, and unravel the institutions needed for recovery. Other threats such as climate change, pandemics, or AI are serious, but nuclear war remains the most immediate and direct route to sudden global civilization collapse and possible human extinction.