World War I, which lasted from 1914 to 1918, was a major conflict involving many countries in Europe and beyond. The main cause of this war was a combination of various interrelated factors, including nationalism, imperialism, military alliances and militarism. Nationalism, especially in Eastern Europe and the Balkans, created tensions between countries with different political aspirations. An attack on Serbia’s political architect, Archduke Franz Ferdinand, on June 28, 1914, was the immediate trigger that resulted in a series of declarations of war. Imperialism also worsened the situation. European nations competed for colonies in Africa and Asia, creating resentment and rivalry. In this context, military alliances, such as the Triple Alliance (Germany, Austria-Hungary, and Italy) and the Triple Entente (France, Britain, and Russia), escalated the conflict when one of the countries became involved, drawing other countries into the war. Militarism, meaning an increase in military power and excessive preparation for war, causes countries to strengthen their armed forces and prepare for military solutions. The impact of World War I on Europe was profound and far-reaching. First, the war drastically changed the political map of Europe. Four great empires – Austro-Hungarian, German, Ottoman, and Russian – collapsed. New states emerged, including Czechoslovakia, Yugoslavia, and Poland, resulting in major social and political changes. In addition, the war had a severe economic impact. Many countries experienced major losses, both in terms of resources and infrastructure. The war sparked high inflation and caused economic recession in many regions. People suffer from food shortages, unemployment and economic difficulties. The spread of socialist and communist ideas also increased amid popular dissatisfaction with post-war conditions. From a social perspective, war changes the structure of society. Women’s roles underwent a significant transformation as they replaced men who went to war in industrial jobs, paving the way for the women’s rights movement. Post-war, many veterans face physical and mental trauma, which adds to the social burden. The cruelty and senselessness of the war, as well as peace treaties, such as the Treaty of Versailles, created a deep sense of resentment in Germany, which in turn became one of the factors leading to World War II. The clash between defeated and victorious countries created instability in the following decades. Thus, World War I was not just an armed conflict, but was also an event that changed the world order, with impacts that are felt to this day. The tensions caused by the war continue to influence international relations, serving as a reminder of the importance of diplomacy and peace in the modern world.