Fall of the Western Roman Empire
The excavation of the Harappa, Mohenjo-daro and Lothal sites of the Indus Valley Civilisation (IVC) in the 1920, showed that northern India already had an advanced culture when the Indo-Aryans migrated into the area. The theory changed from a migration of advanced Aryans towards a primitive aboriginal population, to a migration of nomadic people into an advanced urban civilization, comparable to the Germanic migrations during the Fall of the Western Roman Empire, or the Kassite invasion of Babylonia.