Where does the U.S. have troops in Africa, and why?

The deaths of four U.S. soldiers in Niger earlier this month -- and the ensuing controversy surrounding President Trump's calls to their families -- has thrust a little-discussed country into the spotlight, and could lead to a reevaluation of the U.S. presence on the African continent more generally.

The Pentagon has slowly been bolstering the U.S. presence in Africa in recent years to partner with African nations to thwart various extremist terrorist organizations like the Islamic State of Iraq and Syria (ISIS), Boko Haram and al Qaeda. The four troops slain in an ambush earlier this month -- Sgt. La David Johnson, Staff Sgt. Bryan Black, Staff Sgt. Jeremiah W. Johnson and Staff Sgt. Dustin Wright -- were in Niger to help the Nigerien government fight extremists. 

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The U.S. has roughly 800 military personnel temporarily deployed to Niger, and rough 6,000 military personnel spread across the continent, according to U.S. Africa Command (AFRICOM). Many of those troops are there to support African partners, alongside allies like France, with the goal of increasing the African nations' own security capabilities and stabilizing the region. AFRICOM only began initial operations 10 years ago, in October 2007.

Niger offers a glimpse of that growing presence. In February 2013, former President Barack Obama announced a 40-person increase in Niger, bringing the total number of U.S. military personnel to 100. Back then, Obama described it as an "intelligence collection" mission. Now, the number of soldiers in the country is eight times higher.

A handful of African nations host the bulk of U.S. military personnel, who are generally deployed on rotations for a few months at a time. Djibouti, situated across the Gulf of Aden from Yemen, is one of the world's smallest countries but currently hosts more U.S. military personnel than any other African nation. Roughly 4,000 U.S. military personnel on the continent -- are temporarily deployed to Djibouti.

U.S. troops have been in Djibouti for years. Camp Lemonnier is the only permanent U.S. base in Africa, and serves as a key outpost for surveillance and combat operations against al Qaeda and other extremist groups in the region.

The country with the second most U.S. military personnel deployed there is Niger, with roughly 800, according to AFRICOM. Next comes Somalia, Djibouti's neighbor, with roughly 400 U.S. military personnel. The fourth nation in terms of U.S. military personnel is Cameroon, with more than 100.

The U.S. does have some military presence in virtually every African nation, even if it's small. Most nations, according to June figures from the Pentagon, have at least a handful of active-duty personnel temporarily deployed there.

The U.S. strategy in Africa, as Defense Secretary Jim Mattis has said, is mainly to equip African forces and help allies like France abroad to build those nations' security capacities, and stabilize the region.

"We call it foreign internal defense training, and we actually do these kinds of missions by, with and through our allies," Mattis said on Thursday.

Violent extremist groups based in northern Mali and across the Sahel region in Africa, have proven to be resilient, flexible and capable of carrying out attacks across the border, according to AFRICOM. The groups there have relative freedom to move around, making attacks easier and posing a threat to Niger, other African countries and U.S. military personnel. 

Marine Corps Gen. Thomas D. Waldhauser, commander of U.S. Africa Command, called Africa an "enduring interest" for the U.S. 

"Africa is an enduring interest for the United States," he said in a statement provided by AFRICOM. "Small, but wise investments in the capability, legitimacy, and accountability of African defense institutions offer disproportionate benefits to Africa, our allies, and the United States, and importantly, enable African solutions to African problems."