The World Wars refer to two major global conflicts that occurred in the 20th century. The first, known as World War I, lasted from 1914 to 1918 and involved many countries, primarily in Europe. It was triggered by the assassination of Archduke Franz Ferdinand and resulted in significant political changes and the loss of millions of lives. The second conflict, World War II, took place from 1939 to 1945 and was even more widespread. It began with the invasion of Poland by Nazi Germany and involved numerous nations, including the United States, Soviet Union, and United Kingdom. This war led to the establishment of the United Nations and significant shifts in global power dynamics.