Crises, defined as a period of acute stress on social systems of all kinds, are a recurrent feature of history. As such, they are best approached and understood from a comparative historical perspective. We can distinguish between those caused or precipitated by an exogenous shock and those that derive from an endogenous process that culminates in the crisis. Crises can be of short or long duration and range from local to global. The most severe are ones that lead to a civilizational collapse or radical simplification process. Historically, severe crises have been localized to specific parts of the planet, even when several occur simultaneously because of global natural phenomena, but in the modern world we have truly global crises. Evidence suggests that such a global crisis is imminent or has already commenced. This raises practical and normative pressing issues.
