The two “ghost ships” discovered sailing towards the Italian coast last week with hundreds of migrants – but no crew – on board are just the latest symptom of what experts consider to be the world’s largest wave of mass-migration since the end of the second world war. Wars in Syria, Libya and Iraq, severe repression in Eritrea, and spiralling instability across much of the Arab world have all contributed to the displacement of around 16.7 million refugees worldwide. A further 33.3 million people are “internally displaced” within their own war-torn countries, forcing many of those originally from the Middle...