Historian Joanne B. Freeman’s first book was about political violence amid the founding of the American republic. Subsequent research into an 1838 duel took the Yale professor further into the 19th century, the period leading up to the Civil War. It was an extremely violent time — even in Congress. “The more I looked,” Freeman said, “the more I found.”

In her new book, “The Field of Blood,” Freeman chronicles the fisticuffs, brandished weapons, and bloodshed that took place in Congress in those years. While Boston readers may be familiar with the brutal caning of Massachusetts Senator Charles Sumner, this was not an isolated incident. As in Sumner’s case, Freeman said, the fights were generally sectional, and often escalated to physical violence by Southerners. As war drew closer, increasingly the fights were about slavery.

When it came time to tell the story, Freeman said, she looked for a narrative guide through the 19th-century antebellum thickets. She found one in Benjamin Brown French, a New Hampshire native and Washington fixture who left behind an 11-volume diary, scads of journalism, letters, and poetry. As an added bonus, she added: “He had a sense of humor; he’s really observant; and he recorded a lot of detail about the fighting. He ended up being an ideal source.”

Parallels between that time and ours are increasingly clear. “Both then and now we have extreme polarization, distrust of national institutions, extreme rhetoric, conspiracy theories,” Freeman said. ...