I had been to Atlanta, Ga., before — running trainings with Occupy Our Homes Atlanta as part of the Wildfire Project. But until Saturday, I had never been to Atlanta the day George Zimmerman was acquitted for the murder of Trayvon Martin.

In some ways, it was strange to be away from New York when it happened — the city whose streets I’ve gotten used to marching in, the people I’ve struggled alongside for years, the cops I’ve learned so well. But in many ways, being in Atlanta felt lucky — away from the shiny glass of Wall Street, the manufactured dreams of Times Square, even the quiet Park Slopes that blur our vision and obscure hard truths. Instead, I was in a place where the faces of slave-owning Confederate generals still stand chiseled into the sides of mountains commemorating them, where a sizeable majority of the population is descendant from people kidnapped, enslaved and brutalized ever since. Being in the South felt somehow closer to the truth. But you know what Malcom X said: “Long as you south of the Canadian border, you’re south.”

The first night after the verdict came we marched in the streets, and the march grew with the very real anger and sadness and fear and hope drawing people out to join. The next day was even bigger, in the thousands. We must have marched five miles, much of it in the pouring rain. The city erupted in a symphony of car horns honking in solidarity, echoed by people cheering and clapping from their windows, emboldened by thousands of people stopping on every sidewalk with their fists up, and strengthened by people jumping out of homes, restaurants and cars to join. The music was loud — genuine mourning, righteous fury and deep purpose. I remember thinking, while marching to the beat, that this is the kind of music that revolutions come from.

The sound of the car horns struck me most — in anger, but not anger that they couldn’t get through, all in solidarity and encouragement. I heard from friends who were part of the demonstrations that took over Times Square that even there — in a city where people are so stressed out that they eat while walking — the honking was supportive. Tens of thousands were in the streets in dozens of cities across the country, and the media couldn’t help but report on it. Friends and family who have never identified themselves as political or radical were furious, and many of them took their first steps into a march. Maybe people have had it. Maybe the music is finally getting loud enough.

I suppose it’s like Aura Bogado wrote in The Nation: The question is not whether the Zimmermans of the world (or the rest of us) are white, brown or black; the question is whether we uphold white supremacy or fight to dismantle it. Oddly enough, in this sense, this case is black and white. In a country where a black person is killed by a cop or vigilante every 28 hours, where more black men are in prisons today than were enslaved just before the Civil War, where drones come home to rest after bombing people of color all across the world in the service of U.S. imperialism, you are either for white supremacy or against it.

The honking horns seemed to compel us — white, black and anyone else — to choose a side. They pierced through the wall of white guilt that threatens to handicap some of us, booming: Yes, you are different, your experience in this country is different, and your role in the struggle is different — but you, too, can choose a side.

Rather, You must choose a side.

As the march snaked through downtown Atlanta, the protesters flooded around cars like water. The drivers — the musicians of the day — sat with their windows down, high fiving or clenching a fist in the air. And every so often a marcher would stop at an open window, have a conversation and take down the driver’s phone number to put it on a list for future organizing. At moments like those I was reminded that people don’t march forever, that crisis moments pass and that we must always think of tomorrow today.

The sight of a young woman taking down people’s numbers reminded me how too often we tell ourselves the myth of spontaneity to avoid the hard work of organizing. There is nothing spontaneous about people streaming into the streets. It comes from a rage that builds over years and centuries, the hard work shifting narratives and raising consciousness, the organizing to bring people in and connect groups to one another, the movement-building to create structures to carry us as we fight. And, of course, people join only when an organized community is willing to step off the curb in the first place, ready to go into motion when confrontations are thrust on us and lines are drawn in the sand.

Then I drifted back into the music, an epic score dedicated not just to Trayvon Martin, but also to all the kids carried through the streets those nights by their parents, whose raised fists seemed to declare that they would no longer permit a world in which they were forced to fear for their children’s lives. The horns — and the rest of the music that gives life to our struggles — blasted through Atlanta and all across the country. The tune was unmistakable: Choose your side, organize and take to the streets.