What is an organized, goal-directed effort by a large number of people to promote or resist change outside of established institutions

Social movements

Explanation:

In simple words, A mass movement, also referred to as social movement, can b understood as the loosely structured attempt to accomplish a certain purpose, usually a social as well as political one, through a broad number of individuals. This could be to bring out such a social reform, oppose or reverse it. It is a form of group initiative which may include persons, groups, or both.

   Thus, the correct answer is social movement.

your answer would b. the missisipi river

hope i you : )