World War I or the
First World War was a global conflict between two coalitions: the Allies and the Central Powers. Fighting took place mainly in Europe and the Middle East, as well as parts of Africa and the Asia-Pacific, and was characterised by trench warfare and the use of artillery, machine guns, and chemical weapons (gas). World War I was one of the deadliest conflicts in history, resulting in an estimated 9 million military dead and 23 million wounded, plus up to 8 million civilian deaths from causes including genocide. The movement of large numbers of troops and civilians was a major factor in spreading the Spanish flu pandemic.