The revolutions in North Africa have put enormous strain on a cornerstone of European integration: the free movement of people and commerce in 25 European states under what's known as the Schengen Agreement.
France reinstated long-abolished checks along its border with Italy after waves of undocumented migrants arrived from Tunisia and Libya. It sent hundreds of migrants back to Italy, prompting Rome to issue temporary travel documents to thousands of refugees. The border row sparked outrage with European Union political leaders in Strasbourg, seat of the European Parliament.
"It was a ping-pong game by two governments, by [Italian Prime Minister Silvio] Berlusconi and [French President Nicolas] Sarkozy, on the back of refugees who were, in fact, in trouble," said Guy Verhofstadt, a member of the European Parliament from Belgium who is president of the EU parliamentary bloc of Liberals and Democrats. "A game disastrous for Schengen because by reintroducing internal border checks it contradicts the whole essence of the union and the basic principle of the treaties."
France and Italy called a truce and jointly called for a review of the agreement, which created Europe's borderless world. But now Denmark says it plans to unilaterally introduce enhanced border controls, including more customs officers, spot checks and video surveillance, as part of a coalition deal with the right-wing Danish People's Party.
"We don't want to go back to the times where you had to show your passport," said Soren Pind, Denmark's minister of integration and immigration. "But what we do want to do is to combat drug trade, trafficking of any kind and that sort of criminal activity.
"And if that is done by increased custom activity, where you randomly work your way through without stopping everyone, then I think that's fine."
Pind, who is a member of the ruling center-right Venstre Party, insists the plans to boost customs and border checks are in full compliance with the Schengen Agreement. But European Commission President Jose Manuel Barrosso told the Danes the EU had "important doubts" about whether the border plan was legal. The bloc also warned that if needed it would "use the tools at its disposal to guarantee the respect of EU law."
Europeans began to question whether a borderless Europe was starting to come undone.
Marlene Wind, director of the Centre for European Politics at the University of Copenhagen, says Denmark's proposal is simply political payback to the Euro-skeptic, anti-immigration Danish People's party. She says that unfortunately it has fed the impression that Denmark wants to close its gates to the outside world.
"It's this whole scare tactic that the open borders will see an influx of immigrants, of criminals, of Gypsies," she said. "This is something that they use to appeal to the fear and to the lowest common denominator among these voters. And I think it's pathetic, to be quite frank."
The Schengen Agreement allows for states to temporarily reimpose border controls — as a last resort — under extraordinary circumstances to ensure public order. But European leaders want clarity on what that really means and whether an influx of migrants constitutes a border crisis. The EU has agreed to take up the issue at a summit in Brussels next month.