A Somali police officer arrests a suspected rebel member of the al Qaeda-affiliated al Shabaab among beach goers in Mogadishu. Al Shabaab claimed responsibility for today's pre-dawn attack on a Kenyan university campus near the Somali border. The following gallery examines who is al Shabaab. Here: Somali police officer (R) arrests a suspected rebel member (L) of the Al Qaeda-affiliated al Shabaab among beach goers at the Lido beach north of Somalia's capital Mogadishu March 23, 2012. (Photo by Feisal Omar/Reuters)

A dejected German Grenadier carrying a machine gun on his shoulder in front of a building on fire during the German retreat in Russia. (Photo by Keystone/Getty Images). 1944

In this Tuesday, August 2, 2016 photo released by Xinhua News Agency, people stand on a platform as the Transit Elevated Bus TEB-1 conducting a test run after it unveiled in Qinhuangdao, north China's Hebei Province. The 72-feet long and 25-feet wide Transit Elevated Bus (TEB) powered by electricity can carry more than hundreds passengers, is designed to go over the normal traffic to help ease traffic congestion without having to dig new tunnels or build elevated rail tracks. (Photo by Luo Xiaoguang/Xinhua via AP Photo)

A Kenyan soldier takes cover as shots are fired in front of Garissa University in Garissa town, located near the border with Somalia, some 370km northeast of the capital Nairobi, Kenya, 02 April 2015. At least 15 people have been killed and some 60 were injured in an attack carried out by Somalia's Islamist militant group al-Shabab, according to local media reports. (Photo by Dai Kurokawa/EPA)

A member of Sakura circus team performs during the second day of a one week show in Padukka, near Colombo, Sri Lanka November 28, 2016. (Photo by Dinuka Liyanawatte/Reuters)

Commuters interact with an elephant as he rests in a public road ahead of the annual Perahera festival of the historic Gangaramaya Temple in Colombo on February 18, 2019. Some 50 elephants, most of them from the central area of Kandy along with thousands of traditional drummers, dancers, and monks have gathered in the Sri Lankan capital to participate in the city's biggest two-day annual Buddhist Navam procession, scheduled for February 18-19. (Photo by Ishara S. Kodikara/AFP Photo)

A boy walks with toy guns as people ride an APC during a military show at the Finnish Gulf coast in St.Petersburg, Russia, Saturday, September 5, 2015. (Photo by Dmitry Lovetsky/AP Photo)

Ngorongoro Crater (Tanzania). At 610m deep and 260 sq km, this is the largest unflooded caldera in the world. A blue-green vision from above it's a haven for engangered wildlife and Maasai livestock. The crater was formed three million years ago when a giant volcano, which could have been as high as Kilimanjaro, exploded and collapsed. The caldera formed the concentric fractures in the crust cracked down to a magma reservoir deep underground. (Photo by John Bryant/Getty Images)