The Center for Strategic and International Studies in Washington published in February 2014 an analysis titled "The Reinvention of Al-Shabaab: A Strategy of Choice or Necessity?" by Matt Bryden, director of Sahan Research, a think tank located in Nairobi, Kenya.
In this excellent study, Bryden notes that al-Shabaab's leadership was once relatively heterogeneous, including nationalist and politically pragmatic figures such as Hassan Dahir Aweys and Muktar Robow. There were differences within al-Shabaab over the value of a relationship with al-Qaeda, the wisdom of attacks on civilians, and the role of foreign fighters in the organization. Following a purge of the nationalists, what now remains of al-Shabaab is the more extremist fringe: an al-Qaeda franchise in Somalia, imbued with the "takfiri" ethos that legitimizes the killing of other Muslims, and recommitment to the cause of international jihad and the restoration of an Islamic caliphate.