A few months ago I visited the offices of a charity which supports persecuted Christians.
In the downstairs room there was a vast cache of newly printed books. Tortured for Christ, Operation China and – my favourite – Iran: Desperate for God, were just a few examples of reading favoured by Christians who specialised in exporting their faith to the more dangerous parts of the world.
North Korea is regarded by militant proselytisers (usually American Christian fundamentalists) as the ultimate target, an officially atheist state that is crying out for Christ. It is, however, unusual for foreigners to try and proselytise directly inside the secret state.
Every year thousands of bibles are attached to balloons and floated across the Demilitarised Zone or smuggled from China.
Missionaries floating bibles over the globe's most-heavily fortified border might see themselves as doing God's work. But plenty in the international community are terrified they might inadvertently start World War Three.