I think the measure is pretty simple: when the society is no longer united by a common idea. Look at what’s going on in the US currently: we are the wealthiest nation on earth. This lead to a lack of a common struggle, without which what we have in common is some loose sense of patriotism. But patriotism means “I can do whatever the fuck I want, especially with my guns” for the people on the right, and “this country is fundamentally racist and we should fix that” on the left. A house divided against itself cannot stand.
Contrast this with the last few grand unifying events in the US history: 9/11, the Apollo program, WWII, WWI, the American revolution, etc. When there is a common struggle people are more likely to display patriotism as forgoing exercising certain rights (holding onto all your rubber and copper during WWII in lieu of helping the war effort). When it’s peace and prosperity our brains look for a struggle and if it’s not against an external force, it becomes against each other.