The story has its basis in the enormously successful comic book series CIVIL WAR, in which the world of Superheroes is also torn asunder by the government mandated Registration Act, which means to identify and to register all superheroes among the population. Any superhero who does not comply is therefor automatically branded a fugitive. In the comics this had severe consequences, but this film serves plenty of them already for Steve Rogers and his friends.
The reason for the Registration Act, which in the film is called the Sokovia Accords, is that in the first two Avengers films, a lot of collateral damage and casualties were reported during the New York incident (in the first Avengers film), the Washington incident (in Captain America The Winter Soldier) and in Sokovia (Avengers : Age of Ultron). Also in the beginning of this film, a superhero intervention led by Captain America costs 9 civilians their lives and it is for that reason that the government demands the Avengers to be put under United Nations Supervision. Faced with his own guilt in the death of civilians, Tony Stark acquiesces to the Accords but Steve Rogers does not.
The result is a fantastic action epic, by far the most impressive as well as the longest that Marvel has made so far. Because the film has only just started its theatrical run, I will not give away story details here, go see the film if you like this kind of entertainment.
And there is also plenty of personal surprises for Steve. The action is amazing, the story line is gripping, the music is very effective and although the editing is sometimes just a bit too fast, it does come across as very effective. In all, I would finish with the following information: although there will still be other Marvel Superheroes that will see the day of light on film before the story continues, you will see the next step in the upcoming AVENGERS: INFINITY WAR films.
As for Spider-Man, Black Panther, Ant Man and Natasha, you will be pleased to know that these characters will also soon get their own films again. I can only say EXCELSIOR, and in the words of the immortal Stan Lee (who again has a very funny cameo appearance in the ending of the film) MAKE MINE MARVEL !!!!!
Stan Lee