By strange coincidence system-changing crises tend to happen every thirty years.
A crisis in a politico-economic system is when the practices, behaviour and structures that have allowed the system to reproduce itself are no longer comfortably able to do so. Crises may eventually resolve themselves in the restoration of the current system, or they may lead to the breakdown of the existing system and the establishment of a new state of affairs. The tricky thing is to identify a crisis while it is happening; often, we are only able to identify crises after the event.
Those of us living in the advanced capitalist countries have seen only one system-changing crisis in the period since the Second World War, namely in 1973-80 when the Keynesian political, economic and social consensus - the so-called thirty post-war golden years of growing prosperity - gave way to market fundamentalism in the US, Britain and less dramatically and more slowly in continental Europe.
Are the thirty years of market fundamentalism (1980-2010) coming to an end? Well, if they are, what does the next epoch look like? It's very hard to tell.
Is it merely coincidence that these historical periodisations last thirty years? For instance the years of catastrophe in the mid-twentieth century (1914-1945) also lasted thirty odd years, as did, roughly, the age of imperial monopoly capitalism (1880s-1914).