Before the Avengers split apart from the inside out in Captain America: Civil War, the group can be seen running like a well-oiled machine towards the beginning of the film.
During that scene, Captain America, Black Widow, Falcon, and Scarlet Witch are attempting to stop Crossbones from stealing a bioweapon from a Lagos facility. Noticeably absent are fellow Avengers Vision, War Machine, and Iron Man. As Joe Russo explains, that choice was intentional, and was partly made to show the diverseness of the team (via CinemaBlend).
"We wanted to show that the Avengers were functioning like a military unit now - that they would take specialist into each location dependent on what was required. They're beginning the mission undercover, and it's easy for Wanda and Natasha to be undercover. They have the eyes in the air in Falcon and Cap, so we wanted to kind of create this idea that they're dealing with hotspot issues all over the world. And Vision and War Machine can be dealing with one problem, while they're off in Lagos dealing with another problem. So they divide and conquer using their resources on a mission dependent basis."
In addition to showing how the team adapts to given situations, the Russo's also believed that going with a Captain America-centric group would be the best way to bring viewers into the storyline.
"We thought it would be best to bring back that group from Winter Soldier, just to re-embed you in Cap's story, and obviously Wanda is very story-specific in that sequence. And this is about Cap mentoring her and a tragic mistake that happens, so it made sense that she would become part of that group. But we wanted to slowly expand the group from Winter Soldier, just so you're coming into it from Cap's point of view. You're coming into the storytelling from Cap's point of view."
Captain America: Civil War hits Blu-ray & DVD on September 13th.