There were people prior to the US Civil War that actively committed terrorist acts for the political purpose of ending slavery. Some of those actions arguably galvanized public support for a war. Such as John Brown; his raid on the arms depot in Harper's Ferry was used as propaganda in the south to say that the north would never accept slavery, and therefore the "rational" thing to do was to secede.

We've already seen small far-right groups milling around the edges of terrorism; the Proud Boys, Threepers, Patriot Front, etc. They're pushing the needle.