Its history: Al-Shabab has been terrorizing Somalia for years. Al-Shabab means "the Youth" in Arabic, though the group refers to itself as Harakat Al-Shabab al-Mujahideen. It was once a part of the Islamic Courts Union, a coalition of sharia courts that had gained control of much of Somalia in 2006, though other analysts link its leadership to the Al-Qaida-linked Somali Salafist group Al-Ittihad Al-Islami that fought throughout the 1990s.

Al-Qaida link: After the Council of Islamic Courts was defeated by troops loyal to the Somalia transitional government and Ethiopia in 2007, Al-Shabab fighters retreated to the countryside, where they heeded calls from Al-Qaida to turn to guerrilla attacks and suicide bombings. In 2008, the U.S. government designated Al-Shabab as a foreign terrorist organization.

While many fighters in the group appear to be motivated by nationalist and local concerns, its believed that many of the group's senior members have links to Al-Qaida and may have fought in Afghanistan. In 2012, the group publicly affiliated itself with Al-Qaida's brand of global jihad, and pledged allegiance to Ayman al-Zawahiri.

Other attacks: Al-Shabab has attacked targets outside of Somalia, notably in Uganda and Kenya, prompting the latter to militarily intervene in Somalia in 2011. On Sept. 21, 2013, gunmen seized control of the Westgate Mall in Nairobi, Kenya, prompting a standoff that lasted several days and left the mall devastated. At least 67 people were killed.

The leader: Al-Shabab's leader, Mukhtar Abu Zubeyr, better known as "Godane," is said to have been the mastermind of the Kenyan mall attack. Godane had emerged victorious in a power struggle against rival Al-Shabab commanders just months before. He had at least four of his rivals killed because they did not favor his more internationalist approach to the group's jihadist struggle.

Reportedly born in the breakaway state of Somaliland in 1977, Godane was a bright student and earned scholarships to study in Sudan and Pakistan. He was bookish, eloquent in both Arabic and Somali, recited poetry and quoted from obscure academic journals. He was believed to have traveled to Afghanistan and possibly received military training there.

Upon his return to Somalia, Godane became affiliated with Al-Ittihad Al-Islami, and may have been involved in the murder of a British couple who ran a school in Somaliland. He went on to hold senior positions in Islamic Courts Union, and joined Al-Shabab in 2007, eventually becoming its top commander after a U.S. missile strike killed its supreme leader, Aden Hashi Ayro.

Key to its success: The success of the Kenya mall attack brought the group a renewed focus from the West. Less than a month later, the United States mounted a raid on an Al-Shabab compound in Barawe, ultimately backing off because too many women and children could have been hurt by the ensuing gunfight. While the stated target of that raid was Abdulkadir Mohamed Abdulkadir, allegedly the main planner for attacks outside of Somalia, there were suspicions that Godane was the real target.

U.S. history in Somalia: American intervention in Somalia has a troubled history. In 1993, an attempt by the U.S. military to capture a number of Somali rebel leaders in Mogadishu resulted in two U.S. Black Hawk helicopters being shot down. The ensuing battle between U.S. troops and Somali militia was dubbed the Battle of Mogadishu and immortalized in the book and later the movie "Black Hawk Down." The deaths of 18 U.S. soldiers and hundreds of Somalis led to a public outcry and for years afterward the United States was said to be more hesitant to intervene abroad. Over the past few years, however, the United States has quietly expanded its position in many parts of sub-Saharan Africa; it has a major drone base at Camp Lemonnier in Djibouti that houses 4,000 troops, for example. And while the CIA has maintained a base in Somalia for years, earlier this year a small number of U.S. military personnel were secretly deployed to the country — the first time this has happened since 1993.

Washington Post