Monck's experience in Ireland led to his release. He was made major general in the army sent by Parliament against Irish rebels. Making a distinction (like other soldiers of the time) between fighting the Irish and taking arms against the king, he accepted the offer and swore loyalty to the Parliamentary cause. He made little headway against the Irish led by Owen Roe O'Neill and concluded an armistice (called then a "convention") with the rebel leaders upon terms which he knew the Parliament would not ratify. The convention was a military expedient to deal with a military necessity. When in February 1649 Scotland proclaimed Charles, Prince of Wales, as Charles II, King of Scotland, the Protestant Ulster Scots settlers did the same and following Charles's lead took the Solemn League and Covenant. Most of Monck's army went over to the Royalist cause, placing themselves under the command of Hugh Montgomery, 1st Earl of Mount Alexander.