On May 22, 1856, Preston Brooks strode into the United States Senate chamber and beat Sen. Charles Sumner unconscious with a cane. Brooks, a South Carolina congressman, was retaliating for a speech Sumner had given condemning slavery and personally insulting a relative of Brooks.

Though lasting only a minute, the beating had far-reaching consequences. It pushed Americans one step closer to civil war.

And, as I discovered while researching my book “The Man Behind the Cane: Preston Brooks, Political Violence, and the Road to the Civil War,” it sparked a nationwide debate over free speech, political violence and the relationship between the two.

Speak without reprisal

Northerners denounced the caning as an attack on Sumner’s right to free expression. Even if they thought Sumner’s abolitionism too radical – as most white Northerners did in 1856 – they believed a U.S. senator had the right to say what he wanted without violent reprisal.

Visual images of the caning reflected the Northern take on free speech. In John Magee’s political caricature, “Southern Chivalry – Argument Versus Club’s,” Brooks wields a sturdy stick against a defenseless Sumner, who is clutching a pen in one hand and a rolled-up speech in the other. Winslow Homer’s print “Arguments of the Chivalry” depicts Sumner writing at his desk as Brooks prepares to........

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