Well, by definition a stable country is one without a collapse every few decades!
It happens somewhere quite often, and the number of countries with 100-year uninterrupted continuity of government is shorter than you'd expect - basically the unoccupied Allies, Switzerland, and a few microstates.
I meant that it happens in a given country on average every few decades. I took a somewhat slapdash sample last year and the median time of last violent collapse of government was 01945, 76 years ago. On average it happens in a few countries every year.
Historically, there have been civil wars that threaten government's monopoly on violence every few decades? :o
That surely isn't the experience in most stable countries or is it?