As most of the world celebrates the revolutions sweeping Tunisia, Egypt, and now Libya, Europe is watching with anxiety, fearing an influx of African immigrants. Already in recent weeks, more than 5,000 Tunisians have crossed the Mediterranean Sea on boats and arrived on Italy’s shores. A smaller but still significant number of Egyptians has fled for Europe. And more than 100,000 Libyans and migrant workers from East Asia have left Libya, making their way toward Tunisia and Egypt. But these North African migrants are not Europe’s primary concern. In fact, what Europe fears most is a mass exodus of sub-Saharan Africans to Europe through unpoliced North Africa borders.

In the early 1990s, surging numbers of sub-Saharan Africans tried to leave their civil war—and poverty-ridden countries for Europe. In response, Europe tightened its border controls and dramatically curtailed legal avenues for migration by instituting quotas. Still desperate to escape Africa, the migrants found alternative routes out, and Turkey and the countries of the Maghreb became major hubs for illegal emigration from Africa to Europe: every year, tens of thousands of sub-Saharan Africans arrived in Libya, Morocco, or Tunisia, to recuperate, arrange deals with human smugglers, and climb aboard flimsy boats to Italy or Spain. Many of them died on the journey or were intercepted by European patrols and sent back to Africa. Those who made it joined Europe’s army of irregular workers and asylum seekers. Those who were unable to reach Europe and unwilling to return home remained in North Africa, trying their chances again and again.

In the past decade, European countries started supplementing their own border controls with external gate- keeping agreements with North African dictators. In a 2003 agreement with Spain, Moroccan authorities pledged full cooperation in migration control in return for $390 million in aid. Since the late 1990s, former Tunisian President Zine el-Abidine Ben Ali helped crack down on the transit of migrants through Tunisia in exchange for economic cooperation and preferential trade.

Cooperation between Italy and Libya, a former Italian colony, was particularly intense. In a 2004 bilateral agreement, the Libyan leader Colonel Muammar al-Qaddafi agreed to help prevent sub-Saharan African migrants from using Libya as a country of transit. Pressured by Italy, the European Union lifted its nearly 20-year-old economic sanctions and arms embargo on Libya. The end of the embargo allowed Italy to supply Libya with the high-tech equipment needed to curb irregular migration.

The relationship between Italy and Libya culminated in the 2008 “friendship pact,” in which both pledged to increase cooperation in fighting terrorism, organized crime, drug trafficking, and illegal immigration. Qaddafi agreed to keep African migrants from leaving Libyan shores for Italy and to readmit those intercepted in the Mediterranean Sea. The price tag for this service was $5 billion in Italian investment in Libya and six patrol boats to police the waterways between Africa and Europe.

The Europeans’ tighter border policies and pacts with the North African leaders paid off. With generous funding from Europe, the dictators used their armed forces to keep a growing population of desperate sub-Saharan Africans from entering Europe. Between 2000 and 2004, Morocco alone intercepted more than 80,000 foreigners -- mostly sub-Saharan Africans in transit to Europe. On May 6, 2009, the Italian coast guard and navy interdicted a migrant boat and forcefully returned its passengers to Libya. Italy’s interior minister, Roberto Maroni, hailed the act as a "historic day" in the fight against illegal immigration.

For its part, Libya accepted and then imprisoned the migrants. Human Rights Watch has reported that returned migrants face violence and torture. The organization also reported that Libyan authorities even sold some returned immigrants to human smugglers who kept them in private jails until receiving ransom from their families. And since the current unrest spread to Libya last month, the antigovernment forces attacked many sub-Saharan Africans who were suspected of being mercenaries hired by Qaddafi. Dozens have been killed and many more are in hiding. With no evacuation efforts in place by their own governments, thousands are stranded in refugee camps.

Living in Libya is no longer an option for many sub-Saharan Africans, but neither is returning home. Crossing the Mediterranean to Europe will be their only escape from the violence and instability that surround them. Unlike the past, however, Europe lacks its Libyan border guard; the political turmoil in North Africa has ended the “friendship act” and Italy’s pact with Ben Ali. A return to the days of cooperation on migration control does not seem possible in the near future.

The fall of the North African dictators has deprived Europe of a relatively effective migration policy, one with few viable replacements. In mid-February, following the first wave of Tunisian migration to Europe, Italy offered to send police and security forces to help the interim government with border control. The government refused but later accepted a delivery of radars and boats to be operated by Tunisians. Given the political environment in Tunisia, however, the government’s efforts to combat migration will be at best limited.

The loss of Europe’s partners in North Africa has made the militarization of the Mediterranean Sea the most attractive policy option Europe has for dealing with the current migration crisis. Europe will likely build a virtual fence there by deploying naval forces. Countries may reinforce naval deployments with aerial patrolling. On February 15, the Italy’s Interior Ministry sent a formal request for help with immigration to Frontex, the EU agency responsible for external border security. Days later, Frontex launched Joint Operation Hermes 2011: a deployment of Italian ships; Italian, French, German, Dutch, Maltese, and Spanish aircraft; and experts from across the European Union to combat the flow of refugees from North Africa. And on February 25, NATO held an emergency meeting to discuss the crisis in North Africa and its implications for migration and refugees.

Europe’s track record of migration control in the Mediterranean Sea is cause for worry. Upon interdicting migrants, the Greek coast guard, for example, is known to puncture their inflatable boats and remove their engines, setting the refugees adrift to sink. In violation of the 1951 UN Refugee Convention and EU laws that bar member states from returning migrants to places where their lives and freedoms would be threatened, the Italian and Greek coast guards deport the intercepted migrants into hostile territories.

In the meantime, the European Union has started preliminary talks with Tunisia’s interim government on an agreement that would likely grant Tunisia preferential trade in return for its commitment to curb irregular migration. And the European Union will likely try to develop similar agreements with still stable second-line countries such as Senegal. It may also grant temporary humanitarian asylum to a small number of migrants. For now, however, the majority of the sub-Saharan African migrants will remain trapped in transit, caught between countries they cannot live in and Europe, which is trying to keep them out.