I have devoted many blog posts to the erosion of the middle class, for the specific reason that when the middle class--the layers of the economy between the Power Elites and landless laborers/state dependents--erodes away, the nation/empire is destabilized and descends into crisis.

A society without a functioning middle layer of economic and social activity is not stable, though repression can mask this for a time.

As historian Peter Turchin explained in his book War and Peace and War: The Rise and Fall of Empires, societies that lose the cohesion needed for concerted, collective action collapse, either by failing to meet an external threat or from internal conflicts.