George Kimball was ready for war as soon as the first brick hit his head.

The 20-year-old printer was listening to an abolitionist lecture in Boston’s Bowdoin Square during the 1860 presidential campaign, when a pro-slavery throng tried to shut it down. Kimball was prepared, present as part of a torch-bearing, black-clad bodyguard called the Wide Awakes, who beat the brick-throwers back using their torches as clubs.

As Kimball walked home, blood in his eyes, he wanted “war declared at once.” Years later, having fought his way through from Bull Run to Gettysburg to Petersburg, he still considered that Boston brickbat, “as much a casus belli as was the firing upon Fort Sumter.” For him, it was the embattled right to publicly protest slavery that sparked the conflict — a fight over free speech brought on the war.

Today, our starkest political debates often turn on similar questions of public speech and public violence. Across diverse conflicts, from college campuses to the Capitol’s steps, we keep asking where the line is between heated words and aggressive deeds. Though framed as a legal question concerning the First Amendment, more often it’s a conundrum for our political culture.

In a democracy, how far is too far?

It’s a question that fueled America’s bloodiest war. The Civil War was fought over slavery (anyone who says it wasn’t is just wrong). But how did American slavery, which began in 1619, spark a conflict in 1861? How did a long-running debate turn into a shooting war? Where, exactly, was that dynamic moment when an argument became a fight?

George Kimball’s Wide Awakes help make sense of it all. That half-forgotten movement provides a missing link between the election and the war. In the presidential campaign of 1860, hundreds of thousands of diverse young Americans joined companies of Wide Awakes, marching in militaristic uniforms, escorting Republican speakers, fighting in defense of antislavery speech. Their grass roots rising helped elect Abraham Lincoln as president, but also began the spiral into war.