I remember reading this theory a bit ago and I thought it was one of the more compelling observations. It depends on whether you're focusing on foreign or domes

I remember reading this theory a bit ago and I thought it was one of the more compelling observations. It depends on whether you're focusing on foreign or domestic politics, because both fit in various ways. When the republic fell to an empire, it was due more to domestic issues: the agrarian middle class was displaced by slave labor and mostly forced into professional military careers, and the very rich infought into conquering the state. The the empire fell (at least, the Western empire) it was foreign issues: the central state was over-extended and unable to hold the full Pax Romana territory any longer. The useful lesson from the "falling Empire stages" is to gracefully cede influence without entering into counterproductive wars with new rising powers, as you mention with China.