This article presents an open model of democratization in the context of discussing some well-known approaches to the role of international factors in democratic transitions. The open model is applied to semi-peripheral states of the international system, more specifically the cases of political change in Spain, Portugal and Turkey in the aftermath of the Second World War. Starting from Dahl's conditions for democratic change, it is argued that the impact of external factors on democratization should be examined closely where the regime expects the internal costs of suppression to be lower than the internal costs of toleration, in other words where the internal balance of forces is unlikely to impel a willingness to democratize. Two new external variables are introduced to open Dahl's closed model: the expected external costs of suppression and toleration. It is shown that, in a democracy-promoting international environment, the leaders of an authoritarian state would base their decisions about whether to democratize on their expectations of both the internal costs of toleration and the external costs of suppression.