In the nineteenth century, war reached its pinnacle of legal prestige, when it attained the exalted status of an ‘institution of international law’. To a degree unequalled any time before or since, it was frankly recognised by international lawyers as an accepted and routine means of conducting everyday international business. In international politics, as well as in economics, it was a laissez-faire era. It was also, in legal terms, a ‘positive’ era – so much so, as to cause the whole nineteenth century to be grandly denominated as the age of ‘positivism’. Positivism was so protean a phenomenon as to defy any neat characterisation. But some of its more salient features may be noted very briefly.