Europe’s Schengen zone celebrates its 30th anniversary this year. It allows citizens of 26 European Union countries to travel and go through immigration or border controls without passports or visa checks.
For many, it is one of the EU’s greatest achievements. Long queues are now a thing of the past for millions of travellers as they can drive or fly through customs unrestricted. That ease of passage, however, has also allowed criminals to boost their activities, and the very real threat of attacks by extremists has forced governments to act.