In his seventh letter List repeated his assertion that economists should realise that since the human race is divided into independent states, "a nation would act unwisely to endeavour to promote the welfare of the whole human race at the expense of its particular strength, welfare, and independence. It is a dictate of the law of self-preservation to make its particular advancement in power and strength the first principles of its policy". A country should not count the cost of defending the overseas trade of its merchants. And "the manufacturing and agricultural interest must be promoted and protected even by sacrifices of the majority of the individuals, if it can be proved that the nation would never acquire the necessary perfection ... without such protective measures."