The Bombing of the Vienna International Centre was a terrorist attack orchestrated by Helmut Zemo in his quest to divide and destroy the Avengers.
Following the Battle of Sokovia, public negativity towards the Avengers and enhanced individuals increased as people around the world demanded for accountability.
After a terrorist attack in Lagos claimed the lives of 26 people, 11 of the victims being relief aid workers from the nation of Wakanda, the international community called for the United Nations to create a system of accountability.
Secretary of State Thaddeus Ross approached the Avengers and informed them that the United Nations was currently in the process of passing the Sokovia Accords, which would serve to supervise the enhanced individuals. Avengers divided over the accords, with Steve Rogers opposing them and Tony Stark supporting them.
Eventually, Iron Man, Black Widow, Vision and War Machine signed the accords while Captain America, Falcon and the rest of the Avengers refused to do so.
The United Nations passed the accords and arranged a formal ceremony at the Vienna International Centre in Austria. Among those in attendance at the ceremony were Black Widow, King T'Chaka of Wakanda and his son, Prince T'Challa.
T'Chaka accepted Black Widow's apology regarding the events in Lagos, but was saddened to hear that Captain America wasn't attending.