The democratic peace is secured not simply (if at all) through explicitly democratic institutions as such, but through a number of social and political norms and institutions commonly associated with democracies. In The Law of Peoples, John Rawls claims that the conditions that secure the peace between democracies can be found in his non-democratic, non-liberal 'decent' societies too. I argue that the situation is more complex than Rawls suggests, but that he is still largely correct. Since decent societies pose no special threat to global peace, then the democratic peace thesis does not justify efforts to democratize them. This argument is part of Rawls’s larger defense of decent societies.
Rawls (as cribbed by Wikipedia in the link above) describes "decent societies" as follows:
He claimed there that "well-ordered" peoples could be either "liberal" or "decent". Rawls argued that the legitimacy of a liberal international order is contingent on tolerating the latter, which differ from liberal peoples, among other ways, in that they might have state religions and deny adherents of minority faiths the right to hold positions of power within the state, and organize political participation via consultation hierarchies rather than elections. However, no well-ordered peoples may violate human rights or behave in an externally aggressive manner. States that do so are referred to as "outlaw states," "societies burdened by unfavourable conditions" and "benevolent absolutisms", and do not have the right to mutual respect and toleration possessed by liberal and decent peoples.
An article on a similar theme argues that it is not enough to look at institutions standing alone to understand how they influence economic and political development. Instead, institutions influence political and economic development in a path dependent way.