Here's an interesting report that was recently featured on Al-Jazeera's English language website. It provides some insight into the rise of the al-Shabaab, also often referred to as the Mujahideen Youth Movement (MYM), as an armed force in Somalia.
Some interesting points/quotes put forth by the author:
1) Entities within the al-Shabaab initially began as a vigilante force fighting criminal gangs and local warlords before 'seeking legitimacy’ by becoming the muscle behind the Islamic Courts Union (ICU).
2) When responding to being placed upon the US list of terrorist organizations an al-Shabaab leader stated, “Al-Shabaab feels honoured to be included on the list… we are on the right path.”
According to my own observations, while the group is a Somali-based organization, they started to receive significant media coverage by Al-Qaeda-affiliated Arabic-language websites last year in the wake of the Ethiopian incursion. Subsequently, Somalia has become an alternative destination to Iraq for some international jihadists.