Complex human societies, including our own, are fragile. They are held together by an invisible web of mutual trust and social cooperation. This web can fray easily, resulting in a wave of political instability, internal conflict and, sometimes, outright social collapse. Analysis of past societies shows that these destabilizing historical trends develop slowly, last many decades, and are slow to subside. The Roman Empire, Imperial China and medieval and early-modern England and France suffered such cycles, to cite a few examples. In the U.S., the last long period of instability began in the 1850s and lasted through the Gilded Age and the “violent 1910s.” We now see the same forces in the contemporary U.S.
