Key moment: In Seattle, protesters gathered on Feb. 15, 2003, to protest the impending U.S. invasion of Iraq.
Historical significance: Millions of people in an estimated 600 cities across the globe participated in the one-day protests. The next month, U.S. forces invaded Iraq to destroy alleged weapons of mass destruction that were never found. College students on campuses such as Stanford University joined in protests for years to come. (Photo by Otto Greule/Getty Images)