World War I, which lasted from 1914 to 1918, was a large-scale conflict that shook the world. The main cause of this war lay in the combination of nationalism, imperialism, military alliances and militarism that developed in Europe towards the 20th century. One significant cause is the nationalism that has hit various countries, especially in the Balkans. Countries like Serbia, supported by Russia, wanted to secede from the Austro-Hungarian empire. The incident of the assassination of Archduke Franz Ferdinand on June 28, 1914 in Sarajevo by Gavrilo Princip, a Serbian nationalist, became the immediate trigger that ignited tensions between the major powers in Europe. After Ferdinand’s assassination, Austria-Hungary issued an ultimatum to Serbia. These tensions sparked a series of declarations of war between countries allied with each other, exacerbating an already tense situation. Germany supported Austria-Hungary, while Russia and France showed support for Serbia. In August 1914, the war officially began when Germany invaded France and Belgium. The impact of World War I was profound. First, more than 16 million people were killed and millions more injured, creating deep wounds in society. This war not only affected the physical condition, but also the psychological condition of many individuals and countries. In addition, the war caused changes in the political map in Europe, with the fall of several large empires such as the Austro-Hungarian, Ottoman, and Tsarist Russia. Economically, the war led to the collapse of many countries. Food producing and industrial countries experienced huge losses due to infrastructure damage. Many countries faced hyperinflation after the war ended, and the Treaty of Versailles in 1919 required Germany to pay enormous reparations, which ultimately contributed to the emergence of an economic crisis across Europe. The social impact is also significant; many women entered the workforce during the war, taking the place of men who had gone to war. This gradually challenged the gender norms of that age and contributed to the women’s rights movement in later years. Finally, World War I created an environment that allowed new ideologies to develop, such as socialism and fascism. Disappointment with the results of the war and dissatisfaction with post-war conditions provided fertile ground for the emergence of political extremism. Overall, World War I changed the face of the world map and marked the beginning of a new era of conflict, including World War II. This conflict reminds us of the importance of diplomacy and global cooperation to prevent a similar tragedy from recurring in the future.