At least 14 peacekeepers, mostly Tanzanian, were killed and 40 injured in a rebel attack on a U.N. base in eastern Congo Thursday night — the worst act of violence on the U.N.'s mission in the country, according to the Washington Post.

The big picure: Close to 300 peacekeepers have been killed since the mission began in 1999, along with hundreds more civilians in the area. The peacekeeping mission in eastern Congo is the largest in the world.