Wakanda is an isolationist nation with a vast deposit of Vibranium beneath it.
Long ago a Chitauri ship crashed in Africa. The Wakandans mined the ship and used the Vibranium to build powerful weapons. The Chitarui, lead by Herr Kleiser, came to the nation trying to get their ship back during World War II, but they were repelled. Kleiser came back and killed T'Chaka, the current Black Panther. T'Challa took over his father's mantle and asked Captain America for help. The Avengers came but the Wakandans defeated them. The Chitauri Command Ship attacked the Avengers' ship and began a siege of the nation. The Avengers returned and destroyed the ship, though Giant Man sacrificed himself and Iron Man almost died.