The Battles of the Boyne and Aughrim were both part of William of Orange's campaign against the Catholic forces of James II in 1690-91. These key battles have passed into the vocabulary of conflict between Protestants and Catholics. This book examines the political events which led up to the campaign then looks at the military facts. It describes the type of weapons used, the military tactics, and explains the fact that King Billy's army was made up mostly of mercenaries from Denmark, Holland and Finland, while King James's army had French and German as well as Irish troops. Englishmen fought on both sides.