The history of the First World War began on June 28, 1914, when the assassination of Archduke Franz Ferdinand of Austria, which was the main trigger of the conflict. This murder was carried out by Gavrilo Princip, a member of the Serbian nationalist group, which demanded independence for Bosnia and Herzegovina from Austro-Hungarian rule. This incident triggered a chain reaction among major European countries. After the assassination, Austro-Hungary issued an ultimatum to Serbia. When Serbia partially refused, Austro-Hungary declared war on July 23, 1914. In a short time, Europe’s complex system of alliances played an important role. Russia, which has strong ties with Serbia, began mobilizing its troops. This sparked a reaction from Germany, which was an ally of Austro-Hungary, and they declared war on Russia on 1 August. Within days, France and England were also involved. The war was marked by extremely bloody fighting on the Western front, including the Battle of the Marne, which halted the German advance into France. This battle shows that this conflict will not end quickly. Trench warfare tactics became common, with both sides locked in prolonged and exhausting fighting. In 1915, Italy, which was initially neutral, joined the Allies. In addition, the war also spread to the eastern front with Russia fighting Germany and Austro-Hungary. In this period, the use of modern technology such as airplanes, tanks, and chemical weapons changed the way war was fought. Following the involvement of the United States in 1917, the situation began to change. The US provided financial support and fresh troops to the Allies, which helped change the course of the war. In 1918, the last German offensive failed, and the Allies began to dominate the battle. The First World War ended on November 11, 1918, with the signing of an armistice. The consequences of this war were far-reaching, including changes in the political map of Europe, the fall of the Ottoman, Austro-Hungarian, and Russian empires. The Paris Peace Conference in 1919 gave rise to the Treaty of Versailles, which set the terms of peace and resulted in Germany suffering territorial losses and heavy reparation obligations. This war left a deep mark on world society and politics. The untold number of casualties, both military and civilian, shows how horrific this conflict is. The transition to a new world after the war became a source of tension that sparked the Second World War just twenty years later. Historically, this event is still being discussed and analyzed to understand its impact on global development.