When it turned 30 in 2017, the Intermediate-Range Nuclear Forces (inf) treaty was ailing. Russia had proposed ripping up the pact in 2005. When it was rebuffed it tested an illegal cruise missile, the 9m729. A few years later the Obama administration called out Russian cheating. In December 2018 America's nato allies belatedly backed America. So, when Russia failed to meet a deadline to destroy the missile this month, America pulled out of the treaty and Russia soon followed. The only pact to ban an entire class of nuclear weapons will thus expire in August. The task for America and nato is to meet the Russian challenge without triggering an arms race that would split the alliance and jeopardise what is left of global arms control.
Under the treaty, America and the Soviet Union scrapped all ground-based missiles with ranges of between 500 and 5,500km (310-3,400 miles), weapons that could quickly reach targets deep into enemy territory. The intention was to remove missiles that strike so quickly that leaders might be panicked into rash nuclear escalation.