Abstract
The article investigates the political and institutional factors that shape the initiation, participation and outcomes of interstate wars. It highlights the importance of political regimes and systems of government, or institutional design. While democratic peace theory has long argued that democracies are less likely to fight and more likely to prevail, this study broadens the perspective by examining the impact of parliamentary, presidential and semi-presidential systems as forms of institutional design. The analysis relies on a dataset of 59 wars involving 153 states between 1919 and 2020, defined according to a threshold of 50 military deaths or 600 personnel per side, which distinguishes substantive conflicts from minor incidents, and assesses the correlations between political regimes, institutional designs and warfare through comparative and statistical methods. The findings indicate that the system of government has no statistically significant effect on the likelihood of initiating war. Yet, parliamentary and parliamentarised systems emerge as the most frequent participants and as the most frequent victors, particularly within democratic settings. The study therefore enhances both the empirical and theoretical understanding of war by showing that the combination of a parliamentary institutional design and a democratic regime is linked to greater military success, at both global and regional levels. While the analysis deliberately excludes other factors such as economic variables or alliance membership to focus specifically on domestic political and institutional effects, it identifies consistent correlations rather than causal mechanisms, thereby providing a basis for future research into the link between internal political/institutional structures and international conflict behaviour.