the Great War
World War I (WWI), which was called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918. It involved all the world's great powers, which were assembled in two opposing alliances: the Allies (centred around the Triple Entente) and the Central Powers (originally centred around the Triple Alliance).
More than 70 million military personnel, including 60 million Europeans, were mobilised in one of the largest wars in history. More than 9 million combatants were killed, largely because of great technological advances in firepower without corresponding advances in mobility. It was the sixth deadliest conflict in world history.
Our ancestors were (unfortunately) there !