A corner stone of the European Union is the Schengen plan which allows any people living in its member states to travel across borders and take up residence in another country. In essence this is the equivalent of any American being able to travel within the boundaries of the United States without encountering the need for a visa. The Schengen concept has created a sense that each person is s member of a “nation” which is called the European Union.
The influx of refugees now threatens the existence of the plan. Greece which is the point of entry for most refugees is furious if other member states refuse to allow refugees to depart from its border. At some point the entire European Union has to make a decision. Or, at some point there has to be a plan to keep refugees from leaving Turkey.
Or, of course, a plan to somehow end the violence in Syria. Good luck. Doubt if even Donald Trump has a Great Plan to solve this problem!