I think breaking the social contract is a symptom. One that produces destructive effects, but not a root cause. It's been a couple decades since I read Tainter's Collapse of Complex Societies, but my recollection of his thesis is societies collapse because the cost of continuing to operate (resolve challenges, keep the various internal processes going) is too high; i.e. either you pay (in resources) more than you get back/save, or the cost of fixing systems it impossible to avoid collapse.