The Nuclear Age is said to be defined by the notion of existential threat. The ability to destroy human societies in their entirety with a single class of weaponry raises profound questions about human existence. It even gives us a new form of species extinction – ‘thermonuclear omnicide’. Unsurprisingly, existentialism was a philosophy that found its feet in the shadow of the bomb. This article explores the possibilities and limits of an existentialist approach to nuclear dangers. It contrasts the views of two figures central to early existentialism: Jean-Paul Sartre and Raymond Aron. Sartre responded to the existential threat of nuclear war with moral outrage about the ‘unreality’ of the Cold War politics driving the arms race and an existentialist call to reject militaristic social norms. Aron, a key figure in early IR realism, famously rejected existentialism and turned instead to outlining norms for an international society that might better restrain nuclear-armed decision-makers. Bringing Sartre’s and Aron’s post-Second World War discussions into the new century, this article argues that the ongoing, and even growing, threats posed by nuclear weapons highlight the limits of Sartre’s approach as a guide to authentic existence in modern life. Instead, it supports Aron’s more conservative approach but also draws on Existentialism to extend it, strengthening the nuclear taboo for the sake of human survival as a persistent but urgent political project. At a moment in IR when scholars and other analysts are once again critiquing the fragile norms of global order and speculating about the dawn of a ‘Third Nuclear Age’, theoretical reflection on the politics of existential threats and the hard choices they entail remain indispensable aspects of IR’s theoretical toolkit. While Sartre and other existentialists argued convincingly that existence precedes essence, Aron reminds us that survival remains a precondition for both.
