Yes, it's a prequel. It tells the story about how the girls were born with superpowers, but they weren't necessarily heroes at the beginning of this movie, so the movie is about the events that happen in their life to make them decide to be heroes. ↗
Playing a character who's dealing not only with a superpower but having a normal relationship is easy to associate with, because I feel that everyone has been through it. ↗
And I hope America will realise, as the only superpower now, it really must use its power in a way that's going to build up the world, and to support the United Nations. ↗