World War I, also known as the Great War, occurred from 1914 to 1918. It involved many countries, primarily in Europe, and was triggered by the assassination of Archduke Franz Ferdinand. The war saw the use of trench warfare and new technologies, leading to significant loss of life and changes in political boundaries. World War II took place from 1939 to 1945 and was sparked by the invasion of Poland by Nazi Germany. This global conflict involved major powers divided into the Allies and the Axis and resulted in widespread destruction, the Holocaust, and the use of atomic bombs on Hiroshima and Nagasaki. The war ended with the defeat of the Axis powers and significant geopolitical changes.