BBC News By Mark Simpson image captionA 12ft statue of Sir Edward Carson was unveiled at Stormont in 1933 The course of Irish history changed 100 years ago with the decision of Sir Edward Carson to stand down from the unionist leadership and relinquish the chance to become Northern Ireland's first prime minister. A century on, his great-grandson believes it was a mixture of personal and political factors which led to Carson's momentous decision, announced on 4 February 1921. A large statue of Carson was erected at Stormont in spite of his reluctance to lead the new parliament in 1921. His great-grandson, Toby Carson, points out that the veteran unionist leader was 66 years old at the time.