World War I - Wikipedia tao Samoa New Guinea Nauru Micronesia British India Kelantan Central Asia Naval theatres U-boat Atlantic Germany Mediterranean Adriatic Eastern Mediterranean Air theatres Britain Constantinople <span>World War I,[b] or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a global conflict between two coalitions: the Allies (or Entente) and the Central Powers. Major areas of conflict included Europe and the Middle East, as well as parts of Africa and the Asia-Pacific. The war saw important developments in weaponry including tanks, aircraft, artillery, machine guns, and chemical weapons. One of the deadliest conflicts in history, it resulted in an estimated 15 to 22 million military and civilian casualties and genocide. The movement of large numbers of people was a major factor in the deadly Spanish flu pandemic. The causes of World War I included the rise of the German Empire and decline of the Ottoman Empire, which disturbed the long-standing balance of power in Europe, the exacerbation of imp