World War I: Australian and New Zealand troops arrive in Cairo, Egypt.

World War I or the First World War, also known as the Great War, was a global conflict between two coalitions: the Allies and the Central Powers. Main areas of conflict included Europe and the Middle East, as well as parts of Africa and the Asia-Pacific. There were 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 30 million military casualties, plus another 8 million civilian deaths from war-related causes and genocide. The movement of large numbers of people was a major factor in the deadly Spanish flu pandemic.

Cairo is the capital and largest city of Egypt and the Cairo Governorate, being home to more than 10 million people. It is also part of the largest urban agglomeration in Africa, the Arab world, and the Middle East. The Greater Cairo metropolitan area is one of the largest in the world by population with over 22.2 million people.