Voter registration activists fanned out in the crowds, signing up thousands of the nation's newest voters.
Hannah Brashers believes grassroots efforts, especially those by young people, can be powerful.
"Can you imagine how it would be to lose someone that close to you?" "This is something we're going to be engaged in fighting long-term".
"I think we're losing the public ..."
"I'm really exhausted of being afraid at school", said Maya McEntyre, a 15-year-old high school freshman from Northville, Michigan, who joined a march by thousands in Detroit. We will take the big and we will take the small, but we will keep fighting. Little children carried signs reading "Protect me-don't kill me", and parents held ones giving the USA elected leadership mid-term grades: "A+ from NRA = F from parents and children".
She says, "I feel like we shouldn't have to do this, but I'm so grateful to be surrounded by so many people who are getting out and are trying to create real change in this country since the legislators won't".
Kasky appeared with other Marjory Stoneman Douglas students on CBS's "Face the Nation".
As a parent I feel frightful for the kids that were killed.
George Clooney and his wife, humanitarian lawyer Amal Clooney, were among the many stars who took to the streets of D.C.in solidarity of the protest.
MR SPENCER ENGLAND, a counter-protester from La Porte, Indiana.
"Politicians: either represent the people or get out".
"This isn't a new issue", Nardi said.
Unfortunately nerves seemed to get the better of her for a moment.
"Because this", he said, pointing behind him to the Capitol dome, "this is not cutting it". "It is common for people to carry guns on a regular basis or see guns on a regular basis".
Zion Kelly, 16, the twin brother of 16-year-old Zaire Kelly, addressed the crowd of student protesters, friends and supporters Saturday.
Television images showed youthful marchers filling streets in cities across the United States including Atlanta, Baltimore, Boston, Chicago, Los Angeles, Miami, Minneapolis and NY.
At the march in Washington, an elementary school student from Virginia, Naomi Wadler, 11, captivated demonstrators when she spoke up for African American girls who were victims of gun violence but whose stories "don´t make the front page".
"It's important because children are dying", said Lafayette High School junior McKayla Weaver.
More than 800 demonstrations were scheduled in the U.S. and overseas, according to coordinators, with events as far afield as London, Mauritius, Stockholm and Sydney.
On the other side of the debate, gun rights advocates cite constitutional guarantees of the right to bear arms. People seem to be furious over the Trump government for being reluctant.
That electoral activism is where it's really going to make a difference, according to Lois Beckett, a reporter for The Guardian who covers gun policy.
Aerial video captured seas of people - in front of Trump International Hotel in NY; in a central square in Tokyo; along the streets of Boston; at a rally in downtown Fort Worth, Texas.
The Republican appeared on CNN's "State of the Union" on Sunday and said: "How about kids instead of looking to someone else to solve their problem, do something about maybe taking CPR classes or trying to deal with situations when there is a violent shooter that you can actually respond to that". I never expected these students to stand up and call for change.