According to the democratic peace theory, democracies are hesitant to engage in armed conflict with other identified democracies. Contrary to theories explaining war engagement, it is a “theory of peace” outlining motives that dissuade state-sponsored violence. The proposition that democracies are more peaceful than autocracies has spawned a huge literature. Much of the relevant quantitative research has shown that democracies indeed rarely, if ever, fight each other, although they are not necessarily less aggressive than autocracies in general. Although, statistically, the probability of war between any two states is considerably low, the absence of war among liberal democracies across a wide range of different historical, economic, and political factors suggests that there is a strong predisposition against the use of military violence between democratic states. According to scholars, the democratic peace theory can elaborate on the empirical phenomena previously explained by the earlier dominant research program, realism in international relations; in addition, the initial statement that democracies do not, or rarely, wage war on one another, has been followed by a rapidly growing literature on novel empirical regularities. This democratic peace proposition not only challenges the validity of other political systems, but also the prevailing realist account of international relations, which emphasizes balance-of-power calculations and common strategic interests.
One of the most prevalent ideas in the literature of international relations (IR) is that domestic political patterns are linked to foreign policy via the concept of political regime (democracy, anocracy, and autocracy). Since the beginning of the 21st century, the regime-type foreign policy nexus has gained ample theoretical and empirical credibility in IR theory. There are four areas of research on regime type and foreign policy: the first considers democratic peace literature focused on authoritarian and democratic foreign policies; the second deals with democratization and war literature that highlights the foreign policies of anocracies; the third uses the common large-N data sets and research design and unpacks democratic and authoritarian regimes (separately) to identify subtypes of each regime type; and the fourth is the so-called politics and war literature. The politics and war literature is fragmented, with authors pursuing separate and evidently incomplete lines of argument. There are three steps for integrating the key insights of the politics and war literature: First is the intensification of domestic opposition to established elites; second, the adoption of new ruling strategies as a means for leaders to cope with rising domestic political crises and to control their hold over the regime; and third, the occurrence of international crises, in which larger aspects of domestic politics persist or emerge and affect decisions involving the threat of war.