The First World War was a turning point in the history of the United Kingdom. The enormous demands of the war, and its vast expenditure (of men, women, and materiel) transformed both economy and society during the war and led to major ramifications afterwards. It was a ‘total war’; one that required the mobilisation not just of the armed services but of society as a whole. This volume focuses on the ways in which the United Kingdom’s home front mobilised for war and the impact of that mobilisation. The key question is: how much did Britain’s economy and society have to change in order to support its war effort? Were there certain areas where change was more pertinent? To what extent were changes already in motion before the war that were subsequently accelerated by the outbreak of conflict? Or did the possibility of ‘total war’ arise from the ways the economy and society had begun to structure themselves before 1914? Embracing the four themes of this volume – politics, economics, society and identity – this chapter establishes what the UK looked like, and the primary issues it faced, in the immediate pre-war period. But first, what did the term ‘United Kingdom’ mean in 1914?