What was the most important historical event of the past 100 years?

One of the most important historical events of the past 100 years is World War II, which lasted from 1939 to 1945. This global conflict involved most of the world's nations and resulted in significant geopolitical shifts, the establishment of the United Nations, and the onset of the Cold War. The war also led to profound social changes, including movements for civil rights and decolonization. Its impacts continue to shape international relations and societal structures today.