Key moment: Thousands mobilized at a March for Our Lives rally in Washington, D.C., on March 24, 2018, after a mass shooting at Marjory Stoneman Douglas High School in Parkland, Fla., left 17 dead. Shooting survivors and others called for stricter gun laws.
Historical significance: Survivors of the Florida shooting started the March for Our Lives movement and organization, which advocates for policies supporting gun reform. Organizers say more than 250 gun safety laws have been passed since the group’s founding. (Photo by Kyley Schultz/Cronkite News)