On April 22, 1970, 20 million Americans hit the streets to protest the environmental effects of more than 100 years of uncontrolled fossil-fueled industrial development. It was the first Earth Day.
What was intended to be a college campus teach-in soon spread to every community and city across the United States. It was and remains the single largest secular event in history. The sheer size of the protest—along with increasing visual evidence of dire health threats associated with air and toxic pollution—soon forced Congress to pass some of the world’s toughest environmental laws, most of which include community right-to-know provisions and allow citizens to sue their government if it fails to enforce the law.
https://ecowatch.com/2016/04/19/earth-day-paris-agreement/ (link is external)