The primary causes of World War I include a complex interplay of nationalism, militarism, and intricate alliances. Nationalistic fervor contributed to tensions, particularly in regions with ethnic divisions. Militarism fostered an arms race among European powers, escalating the likelihood of conflict. The alliance system, which included complicated treaties such as the Triple Entente and Triple Alliance, created an environment where localized disputes could quickly lead to widespread war. The assassination of Archduke Franz Ferdinand acted as the immediate trigger, igniting a series of events that ultimately plunged Europe into a devastating global conflict.