This chapter argues for the central importance of the development of the principle of neutrality in explaining the contours of the nineteenth-century age of industrial globalisation and the waging of economic warfare between 1815 and 1914. It highlights how nineteenth-century imperial expansion and industrial growth were dependent on the ability of industrial states to sustain easy access to the open seas, even in time of war. It describes how the naval powers co-ordinated and negotiated the rights and duties of neutrals and belligerents in international law in such a way as to maximise the financial, industrial and imperial advantages from doing so. It also explains how the principles of war avoidance and neutrality maintenance helped to underwrite the global power of Great Britain and the contours of the Pax Britannica.