Crimea could be Putin’s tipping point in a game of nuclear chicken

Avril Haines, US director of national intelligence, said last week she assessed the likelihood of nuclear conflict to be low, indicating that Vladimir Putin would probably only authorise the use of nuclear weapons if he perceived an existential threat to the Russian state. But what would qualify as an “existential threat”? Most obvious would be a direct clash of arms with the US. The past seven decades have seen multiple military interventions by both powers — from the Korean war through to the current war in Ukraine — often offset by large-scale weapons deliveries to the other’s opponents. But none of these wars have involved any direct combat between US and Soviet (now Russian) armed forces. This mutual restraint is one of the main reasons why no nuclear weapon has been used since 1945....