This paper underlines Vattel's commitment to maintaining the sovereignty of Europe's small states by enunciating the duties he deemed incumbent upon all political communities. Vattel took seriously the threat to Europe from a renascent France, willing to foster an equally aggressive Catholic imperialism justified by the need for religious unity. Preventing a French version of universal monarchy, Vattel recognised, entailed more than speculating about a Europe imagined as a single republic. Rather, Vattel believed that Britain had to be relied upon to prevent excessive French ambition, and to underwrite the independence of the continent's smaller sovereignties. Against those who saw Britain as another candidate for the domination of Europe, Vattel argued that Britain's commercial interests explained why it was a different kind of state to the great empires of the past. The paper goes on to consider the reception of Vattel's ideas after the Seven Years War. Although further research is required into readings of Vattel, especially in the smaller states of Europe in the later eighteenth century, the paper concludes that by the 1790s Vattel was being used to justify war to defeat the gargantuan imperialist projects of newly republican France, in order to maintain Europe itself, and the smaller states within it.