The Irish Brigade comprised three veteran regiments brought over from Ireland by King Charles I and were all largely Irish and Catholic. They had been fighting for some time in the Thirty Years War in Continental Europe and formed the hard core of the Marquis of Montrose's forces in his titanic struggle for control of Scotland for the King. Because of their experience the Irish Brigade were arguably the most deadly unit in Britain at the time,wild and desperate men who knew that defeat as Catholics in a Protestant land could mean execution or worse.