Given the content of the linked article, I heartily recommend taking a peek at Peter Turchin's work on Secular Cycles (1). He also keeps a blog, where he expands on some of the ideas. Not a light reading, though. The best introduction to his work was a book review at now deleted slatestarcodex - maybe it can be retrieved by internet archive.

Based on the dataset he and his colleagues compiled, civilizations big enough for internal dynamics tend to exhibit these characteristics during their stagnation phase:

* stagnating or declining real wages

* increasing rents

* decrease in social cohesion

* increasing inequality

* increasing urbanization (mostly due to no rural opportunities)

* more people pursuing education, arts and crafts in hopes of joining the elite. This sounds as a plus, until you realize it's caused by inability to keep a decent standard of living in traditional occupations

* sharpening intra-elite competition, leading to a gradual abandonment of previous norms. Dirty tricks become more and more commonplace

* crisis amplification - non-issues turn into crises, challenges turn into disasters

* 'overproduction of elites' leads to increasing corruption and rent seeking

* stagnating wages and increasing corruption leads to strain on public finances

Turchin's contribution lies mainly in providing historical statistics to back these claims, the novel mechanics of 'elite overproduction' and 'elite aspirants', and overlaying a secondary generational cycle, when a clique of elites keep power for too long (30-50 year cycle, think of Boomers in US or WW2 veterans in USSR).

(1) https://www.goodreads.com/book/show/8778747-secular-cycles