When news about Black Panther joining the Marvel cinematic universe hit the Web earlier this year, there were many different theories on how he would be introduced prior to his own solo film.
In the recent Avengers: Age of Ultron, director Joss Whedon and company dropped hints about Black Panther’s homeland, Wakanda. There were hints about one of his major villains, Ulysses Klaw, and about Vibranium, which is a common resource to Wakanda. 
According to Sean Erickson of Movie Pilot, “some of the more interesting photos from the set of Captain America 3 have been of a big fight between Cap, Falcon and Crossbones taking place in what is almost certainly Black Panther’s home turf of Wakanda.”
In the past two days, there have been leaked photos of the set and villains. These photos can lead one to think that the Winter Soldier may be in Wakanda on assignment. Maybe he is en route to assassinate the ruler or rulers. From this information, Black Panther could team up with Captain America and the Falcon to take down the common menace.
There was an earlier theory that Iron Man and Captain America would have tried to persuade Black Panther to join their respective causes, but that may not be the case because Spider-Man is rumored to be in the film as well.