The historical period in the title of this book is approximate, because it indicates very broad developments in the social and political history of Europe from the onset of the modern age of nation-states to the eclipse of the European state system following the outbreak of the Second World War. The term European state system, itself, is a convenient shorthand reference to the network of relationships of a handful of continental powers in the police structure of the Continent. For reasons of space the police relations between France, Austria, Germany, and Switzerland are examined most closely; Russia's police influence in Europe is treated peripherally. Great Britain and the United States have been omitted because they were not deeply involved in the continental balance of power in our period. Bohemia is mentioned in our discussion of the Austrian Empire's police problems in the nineteenth century because in the last chapter we deal with Czechoslovakia's struggle against Nazi subversion.

The bulk of my evidence, much of it in the form of excerpts from documents, explains why I am sparing with the space I give to general historical narrative. Police records exist in abundance in many European archives, but they are voluminous and ill-sorted, so that I was forced to proceed by mere sampling more often than I had wanted. Unlike diplomatic papers, whose complete publication after an interval of some thirty years has become routine, many police documents still remain unread despite the wealth of information they contain on the concerns, the conflicts, and the habits of mind of past generations.