World War I, which lasted from 1914 to 1918, was one of the most significant events in modern history. The causes of this conflict are complex and multifaceted, involving political, social and economic factors. Some of the main causes include overflowing nationalism, tight military alliances, and competitive imperialism. The involvement of various countries in alliances such as the Triple Entente and Triple Alliance created tensions that led to large-scale conflicts. The death of the heir to the Austro-Hungarian throne, Archduke Franz Ferdinand, in 1914 at the hands of Gavrilo Princip, a Serbian nationalist, was the immediate trigger for war. Austria-Hungary issued a strict ultimatum to Serbia, which rejected a number of conditions. This triggered a declaration of war, and within a short time, European countries were entangled in the conflict. The impact of World War I was broad and profound. First, this war caused enormous loss of life, it is estimated that more than 16 million people were killed and 21 million were injured. This not only impacted the military but also the civilian population, causing deep trauma in many countries. Politically, World War I brought major changes. The collapse of four empires – Austro-Hungarian, German, Ottoman, and Russian – resulted in the redrawing of new national boundaries in Europe and the Middle East. The formation of new states such as Czechoslovakia and Yugoslavia as well as mandates in the Middle East changed the geopolitical map of the world. The 1919 Treaty of Versailles, although aimed at maintaining peace, actually planted the seeds of future conflict, especially in Germany which suffered heavy losses. Socially, this war brought changes in the structure of society. The role of women in the workforce increased significantly as many men went to war. This paved the way for women’s suffrage movements in many countries after the war ended. The spread of new ideologies such as socialism and nationalism has also had a strong impact, creating political instability in several countries. The world economy was also affected. The war caused many countries to incur large debts and experience high inflation. Europe’s economy, once strong, is now reeling and will take years to recover. The United States emerged as a new economic power on the world stage after stepping into Europe’s financing plans. World War I also changed the way warfare was fought. New technologies such as automatic rifles, tanks, and fighter planes came into use, taking military strategy to a new and more deadly level. This trend continued and became the basis for future military conflicts. Thus, World War I was more than just an armed conflict; it was a milestone that changed the face of the world. Whether in political, social or economic aspects, the impact is still felt today. Awareness of the causes and consequences of this war remains relevant as an important lesson for future generations.