The First World War, which lasted from 1914 to 1918, was one of the bloodiest and most influential conflicts in human history. With over 70 million people involved, the war covered many countries in Europe, Asia, and the Americas. Understanding the background, causes, and impact of these conflicts is critical to assessing how the modern world came to be. One of the main causes of the First World War was a complicated alliance system. European countries were divided into two large blocs: the Triple Alliance consisting of Germany, Austria-Hungary, and Italy, and the Triple Entente, namely France, England, and Russia. Tensions between these countries increased along with increasing nationalism and a widespread arms race. After the assassination of Archduke Franz Ferdinand of Austria on 28 June 1914, the situation worsened. Austria-Hungary issued an ultimatum to Serbia, which it considered responsible for the event. When Serbia did not meet all demands, Austria-Hungary declared war on July 28, 1914. Then, the alliance system came into play, and the countries were drawn into an increasingly widespread conflict. This war was characterized by the use of new tactics and advanced technology. Trench Warfare, or trench warfare, is typical, where soldiers are trapped in long networks of trenches for years in extremely inhumane conditions. New weapons such as tanks, airplanes, and biological weapons exacerbated the impact of war. Major battles such as the Battle of the Somme and Verdun marked heavy losses on both sides, with deaths running into the millions. This conflict also affects civil society at large. Propaganda was used to increase morale and support for the war, while meeting logistical needs became a priority. The economies of the countries involved shifted towards military production, causing significant long-term impacts. The First World War ended on 11 November 1918 with the signing of an armistice. However, a peace settlement resulted from the Treaty of Versailles in 1919, which punished Germany severely. Military restrictions and high reparation obligations were the starting points for the conflicts that preceded the Second World War. The social, political and economic impact of the First World War was profound. Four great empires – Austro-Hungarian, German, Ottoman, and Russian – collapsed. New countries emerged in Eastern Europe, changing the political map of the world. New ideologies, including socialism and nationalism, gained strength, shaping the political direction of the following decades. In Indonesia, the impact of the First World War was also visible. The Dutch colonial government increased its control to prevent disturbances, and the welfare of the people was depressed. However, these global changes paved the way for national revival movements in various corners. Overall, the First World War not only affected the countries involved, but also marked a major shift in the way humans understood warfare and its impact on society. By studying this conflict, we can learn valuable lessons to prevent similar tragedies in the future.