History Ireland Tit-for-tat: the War of Independence in the northern counties open_in_new article, 2012
National Archives UK Letter from General Smuts to Eamon de Valera open_in_new letter, 4 August 1921
Hathi Trust Digital LibraryThe struggle of the Irish people. Address to the Congress of the United States book, January 1921
Flickr - NLIThe shell of the G.P.O. on Sackville Street after the 1916 Rising photograph, May 1916