On April 22, 1970, 20 million Americans––10% of the U.S. population––came out on a single day to demonstrate. What inspired this massive action? Outrage at the air and water pollution throughout the nation. This first gathering was dubbed Earth Day, jumpstarting the modern-day environmental movement. That year culminated in the establishment of the Environmental Protection Agency and the passage of the Clean Air Act. Two years later, the Clean Water Act was enacted.