This chapter discusses different types of international conflicts including wars, disputes, and ideological clashes. It examines theories for what causes conflicts on individual, domestic, and global levels. Nationalism and ethnicity are identified as major forces that influence international relations and often lead to conflicts when groups demand statehood or adjusted borders. Ethnic conflicts sometimes involve ethnic cleansing or genocide. While religion and ideology can exacerbate tensions, they usually do not directly cause conflicts, which tend to have more underlying political or economic drivers.