Suikoden is essentially a game about building a movement, made up of 108 distinct heroes. Final Fantasy VI does something similar with its 14 characters and ambiguous/rotating protagonisthood.
More recently, Watch Dogs Legion was another interesting experiment in movement-building gameplay, but there is much more to be explored here and the theories of action for climate activist movements like Sunrise Movement or Extinction Rebellion could form fascinating gameplay systems, while offering players a tantalizing sense that if enough of us work together, things really can change.