Manus O'Cahan's Regiment of Foot was an Irish regiment which served during the Wars of the Three Kingdoms in the mid-1640s. History Manus O'Cahan's Regiment of Foot was a body of soldiers, many of whom fought in Europe in the early years of the Thirty Years War. Historians such as C. V. Wedgwood refer to them as a 'Gallowglass' (i.e. mercenary) regiment. They were actually soldiers who sailed from Ireland to Scotland to fight for the Royalist cause there. Manus O'Cahan () never set foot in England; all of his fighting took place in Ulster and Scotland. Their European combat experiences made them some of the most experienced soldiers serving in the Civil War. Some of the men involved appear in a letter contained in the Ormond papers in the National Library of Ireland entitled "List of men gone unto the Isles. Sent by the Lord of Antrim to my Lord Ormonde, 15 Nov. 1644". The text reads: Background Macdonald territories in Scotland originally formed a relatively homogeneous unit with those held by their Irish cousins the MacDonnells in County Antrim. With the loss of the Lordship of the Isles in 1493, these links were severed, leading to nearly two centuries of conflict for their possession, primarily between the MacDonalds, the McLeans and the Campbells. The Hebridean isles of Islay and Colonsay had been held by the MacDonald leader Colkitto, whose mother was an O'Cahan but in 1614, the Scottish Crown transferred ownership to the Campbells in return for pacifying them. Religion was another cause of tension; the Protestant Reformation created a Calvinist Church of Scotland and by 1640, Catholicism was largely restricted to Gaelic-speaking areas held by the MacDonalds in the remote Highlands and Islands. Conflict between the Episcopalian Charles I and the Scots ended with the 1638-1639 Bishops' Wars and installed a largely autonomous Covenanter regime. In Ireland, the post-1609 Plantation of Ulster dispossessed traditional Irish landholders like the MacDonnells in favour of Protestant settlers, many of whom were Scots. Political instability and a desire to reverse these losses resulted in the 1641 Irish Rebellion; the Covenanters originally remained neutral in the 1642-1651 Wars of the Three Kingdoms but sent troops to Ulster to support their co-religionists and the bitterness of this conflict radicalised views in both countries. The Royalists hesitated to use Irish troops outside Ireland but by 1644, the war in England was turning against them;