The book which follows is a study of political extremism in the Spain of the Second Republic and the Civil War: to be precise, of that traditionalist subspecies of right-wing extremism which in Spain was – and is – represented by one of the curiosities of contemporary European history, namely Carlism. In the narrow context of the 1930s, Carlism's most obvious importance resides in its role as a vital element within Nationalist Spain, one without which, indeed, the rebels of 1936 might never have established the military position from which they were able to win the Civil War. Even before the outbreak of hostilities, however, Carlism had played a significant part as one of the political forces most antagonistic towards the Second Republic. As such, it not only contributed its own share in the undermining of that regime, but also by virtue of its existence helped to tug other, less automatically reactionary forces away from the path of constitutionalism.

Yet there is more to Carlism than this. The 1930s marked the centenary of a movement which had throughout that time exercised a powerful influence upon Spanish history, either directly or as a point of reference for other parties, interests and ideologies. In a broader, European setting, Carlism represents the outstanding example of a popular movement of the ultra-conservative, as distinct from the fascist right. Fascism has been intensively studied in recent years, ultra-conservatism or traditionalism less so; study of a traditionalist movement of so classic a type as Carlism may therefore enhance appreciably our understanding of the extreme right in all its forms.