According to Armitage "Rule, Britannia" was the most lasting expression of the conception of Britain and the British Empire that emerged in the 1730s, "predicated on a mixture of adulterated mercantilism, nationalistic anxiety and libertarian fervour". He equates the song with Bolingbroke's "On the Idea of a Patriot King" (1738), also written for the private circle of Frederick, Prince of Wales, in which Bolingbroke had "raised the spectre of permanent standing armies that might be turned against the British people rather than their enemies". Hence British naval power could be equated with civil liberty, since an island nation with a strong navy to defend it could afford to dispense with a standing army which, since the time of Cromwell, was seen as a threat and a source of tyranny.