CEP Senior Advisor and former UK Ambassador to Ireland Sir Ivor Roberts writes: "It is too easy to be smug about the relative peace that has prevailed in Northern Ireland over the past 20 years. The threat of a return to violence in Northern Ireland has thus hung over the Brexit negotiations like a dark cloud. Recent dissident republican activity in Derry is the physical manifestation of this hazard. We need to recognise the extent to which the world has changed since 1998. A new era of technology enables dangerous pockets of extremism to survive – and thrive – even with moderating factors all around. Encrypted communication tools mean extremists can cloak their communications from security services with more ease than ever before. Social media provides an outlet for propaganda that legitimises and reinforces dehumanising violent ideology."