From being a blank spot on the map, the Sahara now looks like a springboard for the advance of militant Islam.

Until recently Mali was famous only for its music and for Timbuktu “” our nickname for nowhere. Suddenly the French are invading this huge, poor, sparsely populated, landlocked African country, much of which is empty desert. Britain is helping them (if we can get our aircraft to fly).

Just a couple of years ago Mali was held up by Western aid donors as a success. It had been relatively democratic since the Malians overthrew a dictatorship in 1992. And despite being poor “” its main earners are gold and cotton “” it functioned better than many of its neighbours. But last March there was a coup and now its Government is ineffective. What went wrong?

First, the Government was not in fact as good as the donors proclaimed. Basking in Western aid and praise, it became complacent, corrupt and did not deliver development, especially in the poor North of the country. Sensing discontent among the population, a young army captain, Amadou Haya Sanogo, seized power last year. Although he was forced to accept a civilian president and prime minister and prepare the country to return to democratic rule, he remains a powerful but unaccountable player.

Second, the North of the country, the Sahara desert, has been home to Salafist rebels pushed out from Algeria in the late 1990s and targeted by militant Islamist movements inspired and funded by Saudi Wahhabi Islamic fundamentalists, preaching jihad against the West.

Like many, my first reaction was that they were welcome to live in the desert. What damage could they do there? But the desert, flat and empty, is also like a sea, in that people can cross with few natural obstacles and no visible state boundaries. It is perfect for smuggling money, drugs, cigarettes, guns and people across vast distances and several borders. Foreigners were, and still are, often kidnapped.

The desert was also home to the Tuareg, tough camel-riding nomads with their distinctive blue turbans, who managed the trans-Sahara trade. Traditionally they were like an aristocracy, keeping themselves apart from the black Africans to the south and frequently enslaving them. But droughts in the 1980s and 1990s destroyed their herds, and many of the young Tuareg went north to join Colonel Gaddafi’s Army.

When he was overthrown in 2011, they grabbed as much weaponry as they could and headed back to Mali, planning to seize the North and declare it an independent country called Azawad. They found well-funded allies in the Islamists and launched their rebellion in January last year, pushing the Malian Army back before taking the entire North of the country and declaring it independent shortly after Captain Sanogo’s coup.

The Tuareg may have had the guns but the Islamists had the money and a strategy. The Islamists also started destroying historic Islamic shrines and, apparently, the ancient libraries of Timbuktu. Well armed and battle-hardened, they then turned on their Tuareg allies and routed them. The Tuareg nationalists have now called off their demand for an independent state but they have made themselves unpopular.

Suddenly from being a blank space on the map, the Sahara from Senegal in the west to Somalia in the east is beginning to look like the springboard for a new Islamist offensive by AQIM (al-Qaeda in the Islamic Maghreb) and other Islamist groups. Mali borders seven African countries; next-door Niger, an equally fragile state, another five. According to Africa Confidential, a well-respected newsletter, the Islamists are targeting Mauritania next, with its rich fishing grounds and mineral wealth, and then Niger, which has uranium and oil.

But the biggest prize would be the destabilisation of Nigeria to the southeast, shortly to take over from South Africa as Africa’s biggest economy and chief foreign supplier of oil for the US. Nigeria already has its own Islamist insurgency, Boko Haram, which has received weapons and training from AQIM. In 2010 Boko Haram bombed the UN headquarters in the capital, Abuja, in the centre of the country, and has attacked churches and government buildings in northern cities. But it has not yet hit targets in the mainly Christian south.

There are reports that the Islamist groups are fighting among themselves, which may happen if all the attacks are in Muslim areas. Most of this part of Africa was traditionally Sufi Islamic “” tolerant of local practices that are blasphemous to strict Wahhabi Islam. Shrines and tombs of local holy men and saints are now being desecrated and women forced to stay at home and wear the full hijab in public.

In Mali women have traditionally played a substantial role in public affairs and dressed in bright colours, their hair often uncovered. But today they wear black or drab green or brown and are forced to stay at home and are only allowed to meet a man if accompanied by a male relative.

Last week Islamist rebels in Mali began to advance south towards the capital, Bamako, taking the key town of Konna. The French realised that the Malian Army was incapable of stopping them and launched their own counter-attack by air.

Mali was part of their African estate and until recently France has remained engaged with its former territories far more closely than Britain has. Since 2006 the US has taken the lead on opposing Islamic militancy in Africa, establishing military training missions in most countries bordering the Sahara. One of the most alarming outcomes of the Mali episode is that most of the US-trained troops are reported to have either stayed in their barracks or deserted and joined the Islamists. But now the US cannot give direct military support to the Mali government because, under US law, it can only give such aid to democracies.

Can this rebellion be stopped by air attacks? Bombing arms dumps and concentrations of rebels may hinder their advance but AQIM can only be quelled by troops on the ground who have the support of locals. At present the Malian Army is weak and lacks morale. That means the French will probably have to provide the core of a force that includes soldiers from other West African countries. They may get help from Tuareg nationalists but they remain untrusted.

Laurent Fabius, the French Foreign Minister, has said the action in Mali would be over “in a matter of weeks”. These are words he may regret.

This piece was previously published in The Times.

Richard Dowden is Director of the Royal African Society