(L to R) Slovakia's Prime minister Robert Fico, President of the European Council Donald Tusk and European Commission President Jean-Claude Juncker deliver a joint statement after the European Union Summit of 27 Heads of State or Government in Bratislava, Slovakia on September 16, 2016. The 27 leaders -- minus British Prime Minister Theresa May -- gathered at Bratislava's towering castle overlooking the River Danube, determined to respond to the challenges of mass migration, security, globalisation and a stuttering economy. / AFP PHOTO / StringerSTRINGER/AFP/Getty Images