As tens of thousands of asylum-seekers and migrants knocked at the door of Germany’s borders, the country’s Chancellor Angela Merkel welcomed them. “Wir schaffen das,” she said — “We can do it!” Her optimism mirrored an earlier enthusiastic welcoming, when in 1989 West Germany’s Chancellor Willy Brandt declared “What belongs together now grows together!” — opening a path for the country’s unification. Germany’s optimism, or at least the optimism of its governing elites, can brush up against the brute difficulty of the task to accommodate a new geopolitical reality not of Germany’s making. Migration threatens to become the make-or-break issue for the European Union. Last September, Merkel announced Germany would re-introduce border checks with Austria, citing the record number of refugees stretching the system to a breaking point. Others followed. Austria began border controls with Slovenia and Norway said all ferry arrivals from Sweden, Denmark and Germany would be subject to checks. When the Schengen Agreement was signed 31 years ago, the goal was to get rid of physical border checks and controls. As it expanded, it became an integral part of the EU and the free movement of people sits at the heart of the single market ideal. But civil war in Syria, along with unrest in the Middle East and Africa, has touched off an unprecedented crisis for Europe. In just three years, the number of asylum-seekers quadrupled from about 300,000 in 2012 to 1.3 million in 2015, according to estimates from the United Nations. And immigration continues to be one of the most divisive and emotional topics on political agendas. In Germany, the populist Alternative für Deutschland, which has been highly critical of Merkel’s refugee policies, is now in 10 of Germany’s 16 state Parliaments and is expected to win seats in the federal Parliament next year. Brexit in the UK. Donald J. Trump’s victory on the back of anti-immigrant rhetoric has propelled far-right movements in Hungary, Austria and France, where Marine Le Pen is now seen as having a chance of winning next year’s election. The United Nations predicts nearly nine million will be displaced inside Syria by the end of 2016. Security issues in other Middle Eastern countries such as Afghanistan and Iraq will continue to push people out. Africa is expected to double its population by 2050, which combined with economic, political and security challenges facing many countries in the continent could lead to massive flows of refugees and migrants to Europe, Stefan Lehne, a visiting scholar at Carnegie Europe, has said. How will the migrant crisis re-shape Europe, its identity and its future? Follow this current to find out.