This book studies the background and development - in Spain, Flanders, England and Ireland - of a traffic in fighting men. It discusses the strategic and ideological features of civil wars in England and Ireland, which took place within the greater European conflicts being fought out by Spain and its enemies. New data from Spanish archives has permitted a stringent testing of numerical estimates of soldiers transported, made by the contemporary observer, Sir William Petty.

The core of this book traces the fortunes of the army created by Owen Roe O'Neill - the victors of Benburb, acclaimed by one poet as the 'Fianna Fail' - from its surrender at Clough Oughter to its disappearance over the horizon of history on the march across Spain. The author vividly recreates the privations of war, life and death, undergone by these men during a twelve-month journey to a distant, 'eastern front'.

The names of many of the Fianna Fail are now recorded; and the extent of Spain's dependence on them (and thousands of their fellows) is revealed.