Bombing of the Vienna International Centre

The Bombing of the Vienna International Centre was an event orchestrated by Helmut Zemo in his quest to divide the Avengers.

Background
In the wake of the Ultron Offensive, public opinion of the Avengers worsened as people around the world demanded for accountability.

Following a terrorist attack in Lagos that claimed the lives of numerous Nigerian civilians and several relief aid workers from Wakanda, several international politicians, among them King T'Chaka of Wakanda, called for the United Nations to create a system of accountability.

Newly-promoted Secretary of State Thaddeus Ross informed the Avengers that the United Nations was in the process of passing the Sokovia Accords, which would serve to monitor and police the increasing number of enhanced individuals.

The team immediately became divided over the accords, with Captain America opposing them due to his mistrust of the government and Iron Man supporting them due to his guilt over the destruction of Sokovia. Eventually, Iron Man, Vision and War Machine signed the accords while Captan America refused to do so.

Eventually, the United Nations passed the accords and arranged a ceremony at the Vienna International Centre. Among those in attendance were Black Widow, King T'Chaka and his son Prince T'Challa. T'Chaka accepted Black Widow's apology, but was saddened to hear that Captain America wasn't in attendance.

Bombing
To be added

Aftermath
Following the bombing, T'Challa was crowned King of Wakanda. When security footage "revealed" that the Winter Soldier was responsible for the attack, he set out to avenge his father's death.

Meanwhile, Captain America learned about the bombing and headed with Falcon to Bucharest, where the Winter Soldier had been hiding since the Battle at the Triskelion.

The two managed to track Bucky down to a Romanian safe house only to learn that he was completely innocent, and that Black Panther and local law enforcement were also in pursuit. This led to a high-speed chase through the streets of Bucharest, one that resulted in the four being arrested and taken to the Joint Counter Terrorist Centre in Berlin.