This paper has discussed multiple theories and proposals on the causes of war. Kenneth Waltz proposed three layers of analysis for war: individuals, states, and the international system. Differences between cultures and civilizations are one possible cause. The conflict caused by non-democratic countries and the democratic peace theory is another possible factor. Economic factors can also contribute to peace or war. The prisoner’s dilemma can also be seen as a contributor. While none of these can be seen as the answer to why there is interstate conflict, by examining these factors, we can see a clearer picture why there is a conflict between countries, and how these factors interact to create interstate conflict.