Severe budget cuts correlate with a higher incidence of riots, demonstrations, political assassinations and general strikes. On the other hand, peace and education demonstrations seem to be more prevalent in times of budget expansion. This was found in a study by economists Jacopo Ponticelli and Hans-Joachim Voth.
The study further shows that the availability of mass media does not make a difference for the likelihood of discontent translating into disturbances. This finding seems to belie speculations that Facebook would have played a key role in the Arab Spring, and that Blackberries would have contributed to the spread of the London riots. However, the study did find that countries with better democratic institutions are less sensitive to austerity unrest.
In their study, Ponticelli and Voth used a number of datasets including one on social unrest in Europe between 1919 and 2009. They ran a number of tests that suggest that there is indeed a causal relationship between budget cuts and social unrest. (via Sargasso. Photo: Andy Miah / Wikipedia)
UPDATE - the authors have now published an article in the Guardian as well.