Al-Shabaab leaders have allowed few outsiders to gain an insight into the group, so the following information is drawn in part from two reports, the International Crisis Group's Somalia's Divided Islamists, published last year, and the July 2011 report of the U.N. Monitoring Group on Somalia.

What are the origins of al-Shabaab? The group became widely known in 2006 when the Islamic Courts Union (ICU) ousted the warlords that controlled Mogadishu and expanded its influence into other parts of southern Somalia. After Ethiopian troops defeated the ICU, al-Shabaab — which means “the youth” — emerged an as autonomous insurgent force.

Is al-Shabaab homogenous? No. Initially it attracted a variety of Islamist groups opposed to the Ethiopian occupation. After the Ethiopian withdrawal from Somalia in early 2009, command became much more centralised and extremist. But al-Shabaab still relies on a wide variety of interest groups, from global jihadists to local businessmen more inspired by profit that the Qur'an.

How is al-Shabaab funded? The rebels operate a sophisticated and wide-reaching “tax” collection system. The U.N. Monitoring Group estimates that it generates up to $100m (£61m) a year through the control of airports and seaports, and taxes on goods, services, produce and livestock. It also operates checkpoint “fees” and other methods of extortion justified under Islamic almsgiving laws.

What is al-Shabaab's goal? The overriding motivations of the hardline leaders are more ideological than political. With support from foreign jihadis, they view themselves as custodians of Islam. They see Muslims as being in a perpetual state of war with the “infidels,” hence the affiliation with al-Qaeda. Other leaders lower down the hierarchy have strictly national ambitions.

What methods has al-Shabaab used to advance its goals? The rebels have used the internet extensively to promote their radical ideology and to celebrate their martyrs — an important recruiting tool for volunteer fighters from abroad. Militarily, al-Shabaab has been effective in winning territory and in waging guerrilla war against a better-armed enemy. They have used roadside bombs and suicide attacks to devastating effect, and planned and financed a July 2010 massacre in Uganda, when suicide attackers killed 79 people.

Why did the rebels withdraw from Mogadishu earlier this month (Augsut)? African Union peacekeepers and pro-government forces had mounted a strong offensive against the militants, and al-Shabaab leaders said the move was strategic. But there have also been increasing signs of divisions in the rebel ranks.

Where does al-Shabaab go from here? Reports suggest that the al-Shabaab leader, Ahmed Abdi Godane, may have been replaced by Ibrahim Haji Mead, a fellow veteran of the Afghan wars. If true, it is unclear what it might mean strategically. Disagreements within the leadership may take time to reconcile, but there is no suggestion the rebels are close to defeat. Indeed a new campaign of attacks aimed at ensuring Somalia is not governed “according to the whims ... of the western nations and their puppet regimes” seems likely. — © Guardian Newspapers Limited, 2011

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