Advent of Cromwell
O'Neil was successful in the beginning, but in the meantime a great change was taking place in England. The movement had set in which led to the great Civil War, the overthrow of the monarchy for a time, the execution of Charles I., and the establishment of the Commonwealth of Cromwell. Cromwell entered Ireland at the head of what was then regarded as a great army, and his military genius soon carried all before him. Phelin O'Neil was defeated, and was afterwards tried and executed. Owen Roe O'Neil, one of the most energetic, brilliant, and devoted champions of the Irish, died suddenly during the war, and for a long time it was the belief of the Irish, although there seems no evidence to support it, that some of his enemies had contrived his death by poison. His death was a heavy blow to the Irish cause. Cromwell was everywhere triumphant, and a new chapter was opened in the story of Ireland.