World War I, fought between 1914 and 1918, was one of the most significant global conflicts in modern history. The main causes of this war are complex and layered, involving political, social, economic and militaristic factors. One of the main causes is the alliance system that was formed between European countries. Major powers such as France, England, and Russia formed the Triple Alliance to oppose the powers of Germany, Austria-Hungary, and Italy, known as the Triple Alliance. Apart from that, strong nationalism in various regions is also a driving factor. For example, tensions in the Balkans, where ethnic groups fought for independence from larger empires, sparked many incidents that made matters worse. The assassination of Archduke Franz Ferdinand of Austria in 1914 by Gavrilo Princip, a Serbian nationalist, was the immediate trigger that opened this conflict. World War I had a very broad and profound impact. On the one hand, this war resulted in enormous deaths; an estimated 10 million soldiers and 7 million civilians were killed. On the other hand, this war also created significant social changes. The role of women in society changed drastically when they began to enter work fields that were previously dominated by men, especially in the industrial and service sectors. The global economy was also seriously impacted. Many countries experienced severe inflation caused by massive military spending during the war. Defeated countries, such as Germany, also had to face the provisions of the Treaty of Versailles, which required them to pay very heavy war reparations. This contributed to an economic crisis that sparked political instability in Germany, contributing to the rise of Nazism. Political reforms also occurred in many countries after the war. Some countries experienced revolutions, such as the Russian Revolution which overthrew Tsar Nicholas II, replacing him with a communist government. In Western Europe, some monarchies were replaced by new forms of government, creating more democratic republics. This conflict also left deep psychological scars. The sense of distrust between countries increased, creating the conditions that led to World War II. In addition, many countries sought a diplomatic solution through the League of Nations, although in practice this organization was unsuccessful in preventing future conflicts. Overall, both the causes and impacts of World War I were complex and interrelated, showing how historical events can shape the world’s future in unexpected ways. The legacy of this war is felt to this day, coloring existing international relations and global geopolitics.