 A sharp decrease in real tax revenue coupled with a strong need to maintain government spending, together with an inability or unwillingness to borrow, can lead a country into hyperinflation.In 1956, Phillip Cagan wrote "The Monetary Dynamics of Hyperinflation", the book often regarded as the first serious study of hyperinflation and its effects (though "The Economics of Inflation" by C. Bresciani-Turroni on the German hyperinflation was published in Italian in 1931).In his book, Cagan defined a hyperinflationary episode as starting in the month that the monthly inflation rate exceeds 50%, and as ending when the monthly inflation rate drops below 50% and stays that way for at least a year.