Although some action took place in the United States and South Korea, the majority of Black Panther was set in Wakanda, which T’Challa became king of at the beginning of the movie, but then had his crown snatched away by Erik “Killmonger” Stevens, born N’Jadaka.
In the end, T’Challa seized back the throne, but at the end of Black Panther decided to finally reveal Wakanda’s true nature to the world.
After being introduced in 2016’s Captain America: Civil War, T’Challa returned to the MCU this past February to lead his own standalone movie.