Military alliances continue to shape the global security landscape, yet existing research often overlooks the diverse nature of these alliances when examining their influence on states military expenditures. In this thesis, I investigate how four distinct alliance types in offence pacts, defence pacts, consultation pacts, and shallow pacts, affect a country’s defence spending. My main argument is that deeper commitments and military obligations should exert a greater financial burden, thereby increasing military budgets, while alliances that lack these commitments and military obligations should have a minimal effect. To assess these claims, I use an adapted cross-national dataset spanning from 1949-2018 capturing alliance arrangements and military expenditures. I conducted an analysis of the dataset utilizing quantitative methods. Contrary to expectations, the findings reveal that only offensive alliances and consultation pacts have a statistically significant effect on military expenditure, with both demonstrating a positive relationship. Neither defence pacts nor shallow pacts show a statistically significant effect on military expenditure. This result underscores the importance of differentiating among alliance types when assessing the effect that alliances have on military expenditure.