What lessons can be drawn from the analysis of the arguments put forward by States when using force in the nineteenth century? First, it may confidently be asserted that law, beyond morals and politics, held an important role. In fact, whether in the ‘centre’, the ‘semi-peripheries’ or the ‘peripheries’, it seems that States systematically appealed to international law to justify or explain their actions. Sometimes references to international law were very clear and direct, sometimes less so. The Austrian intervention in Naples in 1821, the Spanish-American War of 1898, as well as, to a certain extent, the European intervention in Greece in 1827 and the annexation of Hawaii gave rise to rather ‘theoretical’ debates about the scope and limits of the right to resort to force. In other cases, international law might seem to have played a lesser role, but was always in the background; for instance, when a State claimed to be acting in reaction to a previous violation of law. In all the examined precedents, the intervening Power(s) followed the same procedure consisting in alleging that they were protecting or vindicating their rights, whether they issued from treaties or from customary international law. Fundamentally, all these actions were presented as sanctions of law – i.e. as the exercise of the right to self-preservation.