My personal favorite example to get some perspective is from the book Days of Rage. During the 1970s domestic bombings were a daily occurrence, and at the peak there were over 2000 a year. Even the massive amount of violence in modern day Chicago is nothing in comparison to what was happening as recently as the 90s.
It's an interesting thing how crime rates in the US peaked right after the fall of the Soviet Union and then went into deep decline: It's as if having the visible external enemy was the factor that allowed it to increase, and the post-Cold War paralysis deescalated this process. The Soviet bogeyman was replaced in turn with terrorists, but this too is increasingly seen as a domestic issue of "right wing militia v. antifa", lacking in credible affiliations abroad as the Mid-Eastern interventions have wound down.
And that is perhaps the real source of the frantic polarization: Look anywhere, just not in the mirror.
