The vulnerable world hypothesis (VWH) is the view that there exists some level of technology at which civilization almost certainly gets destroyed unless extraordinary preventive measures are undertaken. The VWH was introduced by Nick Bostrom in 2019 (Bostrom 2019).
Versions of VWH have been suggested prior to Bostrom's statement of it, though not defined precisely or analyzed rigorously. An early expression is arguably found in a 1945 address by Bertrand Russell to the House of Lords concerning the detonation of atomic bombs in Hiroshima and Nagasaki and its implications for the future of humanity (Russell 1945: 89). (Russell frames his concerns specifically about nuclear warfare, but as Toby Ord has argued (Ord 2020: ch. 2), this is how early discussions about existential risk were presented, because at the time nuclear power was the only known technology with the potential to cause an existential catastrophe.)
All that must take place if our scientific civilization goes on, if it does not bring itself to destruction; all that is bound to happen. We do not want to look at this thing simply from the point of view of the next few years; we want to look at it from the point of view of the future of mankind. The question is a simple one: Is it possible for a scientific society to continue to exist, or must such a society inevitably bring itself to destruction? It is a simple question but a very vital one. I do not think it is possible to exaggerate the gravity of the possibilities of evil that lie in the utilization of atomic energy. As I go about the streets and see St. Paul's, the British Museum, the Houses of Parliament and the other monuments of our civilization, in my mind's eye I see a nightmare vision of those buildings as heaps of rubble with corpses all round them. That is a thing we have got to face, not only in our own country and cities, but throughout the civilized world as a real probability unless the world will agree to find a way of abolishing war. It is not enough to make war rare; great and serious war has got to be abolished, because otherwise these things will happen.