It has been argued that Walter Long was the most powerful single voice on Irish affairs in the British government for the critical period from 1916 to 1920. As the leader most committed to a federalist approach to constitutional reform in Ireland, he was a central figure in maintaining a firm stance on Ireland as an integral part of the union and in determining the eventual shape of the union after the First World War.

Chief Secretary for Ireland in the last months of the Balfour government in 1905, a Unionist leader with many friends and supporters in southern Ireland, and a politician who held ministerial office in the wartime coalition governments, Long had great influence in establishing attitudes toward Ireland. John Kendle shows that whatever hopes Irish Unionists cherished of combatting the home rule movement depended in great part on the support of individuals such as Long.

Covering the fifteen years during which Long was closely caught up in Irish affairs, Walter Long, Ireland, and the Union, 1905 1920 provides an analysis of Long's attitudes and actions, and underlines his contribution to the resolution of the political and constitutional dilemma confronting the United Kingdom. Kendle concludes that Long, by advocating a federal solution to Anglo-Irish problems, was a principal architect of the partition of the United Kingdom and the post-1922 constitutional map of the British Isles.