In response to my post on Civil War Scenarios, some commenters brought up the 1960s. I actually do not have to read a history of the 1960s--I can remember them.
One thing people forget about the 1960s is how many of the student protests revolved around silly issues. At my high school, for example, the big item on the radical student agenda was a demand (to which the administration caved in) for a student smoking lounge.
I will grant that the 1960s had more political violence than the current period. I think that this is primarily because the U.S. population has aged. Political violence tends to correlate with a large youth population.
However, I will argue that today's political divisions are more troubling. In the 1960s, people were less invested in their political views and identified less strongly with the major political parties.
Through 1968, the political divide was between the Democratic establishment and the anti-war left. Humorist Mort Sahl captured this when he would describe an anguished liberal-establishment father talking about how hard it was to get out of Vietnam, and a son responding, "Gee, Dad, why don't we just turn the boats around?"
President Nixon changed this dynamic. First, his very presence in the White House served to heal the differences within the left between young and old. Second, he defused the Vietnam War as an issue by (a) ending the draft (b) going to China and (c) turning the boats around. The decade of the 1970s saw the heat on the American political burner turned down.
I would describe the American scene in the 1970s as fissaporous, with people identifying themselves in terms of various identity markers, not so much as Democrats or Republicans. More like a high school, with lots of different sub-cultures.
I see two phenomena today that are more disturbing. First, the government is going broke. That is not a problem that has a simple, "turn the boats around" solution. So I do not see how the fundamental source of today's divisions goes away so easily.
Second, I think more people are invested in their political identity than I can ever remember. In the 1960s and 1970s, people were not as worked up about the Dems and the Reps, and they were more worked up about other things.
UPDATE: This story might be filed under "civil war watch."
An armed intruder, spouting opposition to social conservatism, walked into the Washington headquarters of the Family Research Council on Wednesday and shot a security guard before the wounded guard and others wrestled him to the floor and subdued him until police arrived, authorities said.