This book is volume one of a two-part series. Taken together, the two volumes of A Philosopher at War examine the political thought of the philosopher and archaeologist, R.G. Collingwood, against the background of the First and Second World Wars. Collingwood served in Admiralty Intelligence during the First World War and although he was not physically robust enough to play an active role in the Second World War, he was swift to condemn the policies of appeasement which he thought largely responsible for bringing it about. The author uses a blend of political philosophy, history and discussion of political policy to uncover what Collingwood says about the First World War, the Peace Treaty which followed it, and the crises which led to the Second World War in 1939, together with the response he mustered to it before his death in 1943. The aim is to reveal the kind of liberalism he valued and explain why he valued it. By 1940 Collingwood came to see that a liberalism separated from Christianity would be unable to meet the combined evils of Fascism and Nazism. How Collingwood arrived at this position, and how viable he finally considered it, is the story told in these volumes.