Why Institutions Decay:
".... Political decay was caused by the inability of institutions to adapt to changing circumstances. Decay was thus in many ways a condition of political development: the old had to break down in order to make way for the new. But the transitions could be extremely chaotic and violent, and there was no guarantee that the old political institutions would continuously and peacefully adapt to new conditions. This model is a good starting point for a broader understanding of political decay more generally. Institutions are “stable, valued, recurring patterns of behavior,” as Huntington put it, the most important function of which is to facilitate collective action. Without some set of clear and relatively stable rules, human beings would have to renegotiate their interactions at every turn. Such rules are often culturally determined and vary across different societies and eras, but the capacity to create and adhere to them is genetically hard-wired into the human brain. A natural tendency to conformism helps give institutions inertia and is what has allowed human societies to achieve levels of social cooperation unmatched by any other animal species...." read more here: Francis Fukuyama | The Sources of American Political Dysfunction | Foreign Affairs
