Macedonia is a geographical and historical region of the Balkan peninsula in southeastern Europe. Its boundaries have changed considerably over time, but nowadays the region is considered to include parts of five Balkan countries: Greece, the Republic of Macedonia, Bulgaria, Albania, Serbia (including the Gora region in Kosovo). It covers approximately 67,000 square kilometres (25,869 sq mi) and has a population of 4.76 million. Its oldest known settlements date back approximately 9,000 years. From the middle of the 4th century BC, the Kingdom of Macedon became the dominant power in Greece and the neighbouring regions; since then Macedonia has had a diverse history. The definition of Macedonia has changed several times throughout history. Prior to its expansion under Philip II, the ancient kingdom of Macedonia, to which the modern region owes its name, lay entirely within the current Greek province of Macedonia.