In 1903, as European tensions began to mount, Jean Jaurès, the leader of the French Socialist Party, declared his faith in the possibility of securing a peace that was ‘profound, durable, organised and definitive’. The two ‘great systems of alliances’ which, for now, merely held each other in check, would produce strong and lasting friendships; democracy was extending across the continent and it would not be long before ‘all human groups from Finland to Ireland, from Poland to Alsace’ would discover their ‘moral affinities’ and find ‘reciprocal security’ through disarmament....