“Think globally, act locally.’’ This isn’t just a slogan. It’s a deep conviction shared by a growing number of elected officials, experts and citizens around the world: Cities — especially the large ones — can and must play a leading role in solving the complex problems of our time. This new mission is driven by growing urbanization, which is happening world-wide; more than half of the world’s population now lives in urban areas.

Six days after taking office, President Donald Trump is facing the first international crisis of his administration. And it’s unfolding on Twitter. Following through on campaign promises to crack down on immigration, Trump signed executive orders to both kick-start the construction of a border wall with Mexico and block federal grants for “sanctuary cities“ - jurisdictions that offer safe harbour for undocumented immigrants.