The history of the First World War, which lasted from 1914 to 1918, became one of the most significant events in human history. This conflict was marked by various key events that changed the political, social and economic landscape of the world. One of the starting points of the First World War was the assassination of Archduke Franz Ferdinand on 28 June 1914 in Sarajevo. This incident sparked tensions between Austria-Hungary and Serbia, which was supported by Russia. In the weeks following this event, a series of alliances and treaties drew Europe’s major powers into conflict. Austria-Hungary declared war on Serbia on July 28, 1914, setting off a chain reaction involving Germany, France, Britain and others. The First Battle of the Marne in September 1914 marked a new chapter in the war. Here, allied forces managed to halt the German advance towards Paris, marking the start of trench warfare. The trend of trench warfare haunted Europe for years, resulting in devastating war conditions and heavy casualties. On April 22, 1915, the use of poison gas by Germany in the Battle of Ypres became a surprising innovation and changed military strategy. Although effective, the battle brought awareness to the cruelty of modern warfare. Apart from that, historical moments also occurred in 1916 with the Battles of the Somme and Verdun, which recorded very high casualties but did not produce significant results. In battle at sea, the British and German navies met at Skagen and Jutland. Although the British won the battle of Jutland, German naval power remained and posed a threat. Global developments were also seen with the emergence of United States involvement in 1917 after U-boat attacks on its merchant ships. The decision to join the Allies refreshed military supplies and manpower, contributing to the defeat of the Central Powers in 1918. The Treaty of Versailles, signed on June 28, 1919, was the official end point of the conflict. This agreement, with its harsh conditions for Germany, created discontent there and became the seed for the Second World War. In addition, the First World War exposed deficiencies in political, economic, and social systems in various countries, stimulating independence movements in colonial countries and social change in European countries. In a broader context, the First World War affected the geography of the world, allowing new countries to emerge and modernizing political systems in many places. The 1917 Russian Revolution that produced the Soviet Union was one direct impact. Apart from that, the First World War was also the beginning of the modern era which was marked by technological innovation, changes in art and culture, and the development of new ideologies that would influence many generations after. Overall, The History of the First World War resulted in fundamental changes that not only shaped the 20th century but also provide important lessons that are relevant in understanding modern conflicts.