The foundation of the Marvel Cinematic Universe has always been The Avengers, even before the team had been created. Nick Fury always knew the world would need protectors, and when the time came to assemble, it was the need to protect innocents and avenge lost friends that would bring the team together. Yet, there was a fundamental issue with the team that was established in the first Avengers movie and took on a new life in Avengers: Age of Ultron.
Source：https://www.cbr.com/age-of-ultron-proved-why-mcu-original-avengers-faltered/
