Great power war causes extinction.

This report explores issues at the intersection of international relations, conflict studies, and longtermism.l In it, we draw extensively on the mainstream international relations literature but focus specifically on understanding the potential effects of war on the long-term future. Taking a long-term view focuses our attention on the risk a Great Power war poses to humanity's future potential. Extinction, an unrecoverable collapse of civilization, or a permanent end to humanity's growth and progress would all destroy the long-term potential of our species. We call events that could lead to one of these scenarios existential risks .2 Such an event, if it occurred, would be unprecedented in human history. It would cause unimaginable suffering for everyone alive today and extinguish any possibility for trillions of our would-be descendants to live happy lives.

Some of these global catastrophic risks, like an asteroid impact, are direct risks. By contrast, Great Power conflict is a risk factor: it is connected to multiple other risks, and raising or lowering the amount of conflict affects the seriousness of the threats we face in these other areas. In section 4 of this report we consider several concrete pathways through which Great Power conflict poses a global catastrophic risk. We will sort these pathways into three broad categories.

First, we consider ways in which Great Power conflict poses a risk even without a full-blown war breaking out. For example, a new Cold War could hasten the development of dangerous technologies or cause a breakdown in cooperation that precludes international agreements to mitigate other existential risks. Second, a Great Power war could itself be a global catastrophic risk. In an all-out war between Great Power nations, weapons with the potential to kill everyone on earth or irreparably damage civilization could be used. Or, in the aftermath of a major war, the victorious side could emerge as a global hegemon that is able to use advanced technologies to lock in its sub-optimal values. 3 Third, a Great Power war could weaken humanity and leave us more vulnerable to subsequent disasters, like a serious pandemic.