Can the US really nuke North Korea without starting a world war?

Reuters/Kim Hong-Ji

The test by North Korea this week of its biggest nuclear device yet has rattled more than the world’s seismographs. It now seems a paranoid dictator with an appalling human rights record owns the ultimate weapon.

It is particularly concerning given that the explosion, 10 times the size of the country’s previous test, may well have been the nation’s first two-stage hydrogen bomb. Such a design can pulverise a city, and is easier, per kiloton, to fit onto a missile.

Faced with this, some are suggesting that a pre-emptive strike