Tunisia and Algeria today share one key objective with their European neighbours across the Mediterranean – that of preventing Libya, in the words of the Algerian prime minister Abdelmalek Sellal, from turning into “Libyanistan”. This is the first time in more than half a century that the interests of  leading European countries and the US share a strategic interest in stabilising north Africa.

Tunisia remains the only Arab country which is on the path to democracy. It needs to receive, free of charge, all the military training and essential hardware its European and American friends can muster. The point is reinforced by the ISIS-led suicide attack on the border town of Ben Guerdane on 7 March. That the United States will supply a state-of-the-art electronic surveillance system for the Tunisian-Libyan frontier is welcome.

Algeria, the country’s western neighbour, has since the fall of Ben Ali in January 2011 been helping Tunisia's security forces to fight domestic terrorist groups, notably in the Châambi mountains close to their common border. The struggle is a national, regional and European one alike: were ISIS to gain a real foothold in Tunisia, the repercussions would be felt far and afar - in Algeria and, across the Mediterranean, in Italy, Spain and France.

The European Union has learned from bitter experience that measures to help stabilise southern-rim countries must be preventative and, if at all possible, avoid European or American "boots on the ground". The responsibility to assist Tunisia lies squarely with the Europeans. Barack Obama has made clear that the days of European "free riding" on American military power are over, while reflecting that over Libya he had expected Europeans to be more "invested in the follow-up” after Gaddafi's overthrow than they were. The growing mayhem in Libya is partly the result of Nicolas Sarkozy and David Cameron’s gung-ho behaviour in 2011. Nor did the EU do much to help Tunisia when over a million Libyan refugees poured into Tunisia, an estimated 500,000 of whom are still there.

Tunisia's army is small, though proud of its fighting capacity and respect for democracy. The country’s economy is buffeted by the uncertainty which followed the dictatorship, the injury its important tourist sector inflicted by the terrorist attacks in 2015, and the continuing strikes in its phosphate and fertiliser sector, a major source of foreign income.

The Tunisia test

Transitions to democracy are long-term affairs and especially difficult to manage in such a strife-torn region. The management of Tunisia’s economy since 2011 can be criticised, but the bigger picture must also be held in view. An ISIS base in the country would both stop democracy in its tracks and turn the flow of refugees from the southern Mediterranean to Italy into a flood. Algeria would be badly destabilised, and probably Morocco too. Spain would be directly concerned. The refugee crisis in the eastern Mediterranean, along with the terrorists attacks in Paris and Brussels, have already shaken Europe to its very foundations. Europe simply cannot continue treating north Africa as its forgotten frontier.

Algeria has acted for the past five years as the de facto guarantor of Tunisia’s security, with the armed forces and intelligence services of both countries working closely together. Algeria is aware that ISIS influence in the region would threaten its southeast, which suffered a severe blow in 2012 when terrorists from Libya tried to torch the gas field of Tigentourine. Akram Kharief, arguably the keenest observer of Algerian security affair, argues that Africa’s largest country faces two security challenges: a domestic one, where 700-1200 militants are concentrated in the Kabyle mountain range due east of Algiers, and a regional one, where those further south have been pushed out by the security forces, but have also coalesced around Algeria's frontiers with Tunisia, Libya, and Mali.

ISIS fighters originate in Tunisia and Morocco, and to a lesser degree in Algeria itself. Networks of Moroccans trying to cross Algeria on their way to Libya have been dismantled and flights from Algiers to Tripoli stopped. Other recruits to ISIS in its Libyan base of Sirte include Chechens, Afghanis, Pakistanis and Sudanese, although a majority are from the Maghreb.

Security cooperation between Algeria and the US is good, as it increasingly is with European nations, not least Britain. Algeria was given advance notice of US strikes against the Libyan town of Sabratha in March, and its army supplies fuel to French military vehicles engaged in the Berkhane operation in Mali. The country has emerged as the lynchpin of the fight against ISIS in north Africa. Its armed forces are professional, its intelligence capacity and knowledge of tribal networks across the region unravelled. The collapse in the price of oil and the bitter infighting around the succession of an ailing president certainly cloud Algeria's future, but it is doubtful whether they seriously impair its capacity to fight ISIS. Its diplomats remain, in the eyes of their American, European and Arab peers, of high calibre.

Europe is learning that it must talk to Algeria and Tunisia as equals. It must forge a joint security policy in what is a very complex region. Unilateral western interventions, most of which in the Middle East have ended in disaster in recent years, are a thing of the past. That past stretches back to Napoleon’s invasion of Egypt in 1798. A new security partnership between Europe, the US and north Africa is in the making, notwithstanding the fact that the EU has long given up any pretence of trying to bring Algeria and Morocco closer on finding a solution to the international legal status of the Western Sahara. Here the US is trying, while France simply blocking any attempt the United Nations makes to move matters forward. But the immediate  test is for states to work together to deny ISIS. Tunisia is the crucible.