The group has staged ongoing major attacks within Somalia for years.
Al-Shabab and al-Qaida in February 2012 announced their alliance, with al-Shabab leader Mukhtar Abu Zubair pledging allegiance to the global terror movement. Al-Qaida's 2002 attacks on an Israeli-owned Kenyan resort in Mombasa and an attempted attack on a plane carrying Israeli tourists are believed to have been planned by an al-Qaida cell in Somalia. U.S. officials believe some of the al-Qaida terrorists who bombed the United States embassies in Kenya and Tanzania in 1998 were given refuge in Somalia.
WHERE DOES AL-SHABAB'S MONEY COME FROM?
Before African troops moved in, al-Shabab was making a steady income from duties and fees levied at ports and airports as well as extorting taxes on domestic produce and demanding "jihadi" contributions. A United Nations report estimated al-Shabab's income in 2011 at between $70 million and $100 million. It has lost most of that revenue since it was forced out of Mogadishu and Kismayo. Al-Shabab's only ally in Africa is Eritrea — which backs it to counter its enemy Ethiopia, which also has troops in Somalia. Eritrea denies charges that it helps arm al-Shabab.
Al-Shabab is believed to have fractured over its alliance with al-Qaida, which caused a rift that has grown between core Shabab fighters who believe their struggle should focus on Somalia, and growing tensions with foreign fighters who want to plot a regional terrorist strategy. Analysts think attack on Nairobi's Westgate mall could indicate the extremists are winning that internal struggle. Further divisions are believed to have been caused by the group's decision to ban foreign aid organizations from operating in the country and providing food to save millions of victims of conflict-induced famine. That decision was announced in 2011, when the U.N. said Somalia had the world's highest child mortality rate.