Our low-level long-term civil war is mostly a Cold War, but it flares from time to time. Our high level of general social tension means we have less negotiating space, and easy access to very deadly weapons means that when a balance tips, it tips faster and further.
Compare per capita stats on very low level violent incidents (I.e. bar fights or scuffles) in the US versus Canada. They have 'em, too, but fewer and less intense. It's not just our guns.
Edited because iOS spell-checked badly.
Forward out of darkness, Leave behind the night. Forward out of error, Forward into light. - Inez Millholland