He charts the full scope of Dubliners' military service, far beyond the well-known Dublin 'Pals', with as many as 35,000 serving and over 6,500 dead, from the Irish Sea to the Middle East and beyond.

Linking two conflicts usually narrated as separate stories, he shows how Irish nationalist support for Britain going to war in 1914 can only be understood in the context of the political fight for Home Rule and why so many Dubliners were hostile to the Easter Rising. He examines Dublin loyalism and how the War of Independence and the Civil War would be shaped by the militarisation of Irish society and the earlier experiences of veterans of the British army.