Migrations have occurred throughout history and have played an important part in the peopling of all the areas of the earth. Primitive migrations were usually in search of food, but could also result from physical changes, such as the advance of the continental ice sheets, and invasion by other peoples. The most important migrations in European history were the Gothic invasions (3d–6th cent.; see Germans), the Arab invasions (7th–8th cent.; see Arabs), the westward migration of the Golden Horde of Jenghiz Khan (13th cent.), and the invasions of the Ottoman Turks (14th–16th cent.; see Ottoman Empire; Turks).