Macaulay called it the most important siege in English history and this book investigates how an event in Ireland could take on such a stature. This is a military history of one of the most iconic events in Irish history but one that is often relegated to a level of importance below that of the battles of the Boyne and Aughrim. However, the author argues that King James overall strategy met its real defeat at Derry in 1689 and that the chances of his restoration all but vanished when the defenders of the city managed to hold their own against the Jacobite army. He investigates how the Jacobites might have achieved success but concludes that, without substantial help from the French, their cause was doomed. Louis XIV used James II to distract William of Orange but, had he put more resources into the war in Ireland, especially the French fleet, he might have changed the course of European, British and Irish history.