Driven by national anxieties connected to immigration, the increasing use and duration of internal border controls within Europe's passport-free Schengen area will entrench unpredictability for businesses and travelers, strain economic integration and undermine the long-term stability of the agreement's free-movement principles. On July 7, Poland introduced controls on its borders with Germany and Lithuania to prevent the arrival of irregular migrants. According to the Polish government, the decision is a response to Germany's policy of sending back to Poland irregular migrants who enter the country allegedly from Poland, as well as to prevent the arrival of irregular migrants from Belarus who reach Poland through Lithuania....