The US civil war is not the only time the US has been politically unstable. The civil rights movement, the labor disputes of the 1970s, the economic shocks every decade or so from market crashes all have been moments of instability.
What is January 6th if not a concrete example of recent political instability?
As for foreign policy consistency, 7 administrations takes us back to Reagan... The entire movement to sell out our industrial capacity to China and now the movement to try to reverse that have occurred in this time frame. This is just as important as our endless wars in the middle east, imo.
I don't disagree totally but I felt the need to put some nuance here.
Stability doesn't mean statis. The USA has been remarkably resilient to those minor shocks you listed. It continues to be the most politically stable of all the countries that actually count for anything in international affairs.