Harakat al-Shabaab al-Mujahideen (HSM) ("Movement of Striving Youth"), more commonly known as al-Shabaab ("The Youth") is a Militant Islamist insurgent group fighting to overthrow the government of Somalia. As of summer 2010 the group is said to control most of the southern and central parts of Somalia, including "a large swath" of the capital, Mogadishu, where it is said to have imposed its own "harsh" form of Sharia law. Estimates of al-Shabaab's strength, as of December 2008, vary between 3,000 to 7,000. They are allies with Al-Qaeda.

Al-Shabaab's current de facto capital is believed to be the port town of Barawa Southwestern Somalia.

The group is an off-shoot of the Islamic Courts Union, which splintered into several smaller groups after its removal from power by Ethiopian forces in 2006. The group describes itself as waging jihad against "enemies of Islam" and is engaged in combat against the Somali Transitional Federal Government (TFG) and African Union Mission to Somalia (AMISOM). It has reportedly "declared war on the U.N. and on Western non-governmental organizations" that distribute food aid in Somalia, killing 42 relief workers in the past two years of 2008 and 2009. It has been designated a terrorist organization by several western governments and security services. The current leader is named Moktar Ali Zubeyr .

Because of its opinions and methods, Al-Shabaab, has been compared with the Taliban in Afghanistan and Pakistan.

Despite routinely expelling, attacking, and harassing aid workers, al-Shabaab permits some agencies to work in areas under its control. At the height of its territorial control it implemented a system of aid agency regulation, taxation and surveillance. Where agencies are allowed to operate, this is often due to the desire of al-Shabaab to coopt and materially and politically benefit from the provision of aid and services. Senior aid agency representatives often strongly rejected claims that they talked with al-Shabaab, while aid workers working in al-Shabaab-controlled areas often reported they directly negotiated with the group out of necessity.

Al-Shabaab was known as the most prominent terrorist-organization in Somalia which was succeeded to clear away from the bigger cities of the state by the end of 2013.

While al-Shabaab has been reduced in power and size since the beginning of the Kenya Army's Operation Linda Nchi southern incursion, the group has continued its efforts at recruitment and territorial control. The group maintains training camps in areas near Kismayo in the southern regions of Somalia. One such camp was constructed in Laanta Bur village near Afgooye, which is also where the former K-50 airport is located. On July 11, 2012, Somali federal troops and their AMISOM allies captured the area from the militants.

In October 2017, more than 500 people were killed by twin bomb explosions in Somalia's capital city Mogadishu.

An attack on a hotel in Nairobi, Kenya on January 15, 2019 is attributed to al-Shabaab.

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