Supplanting the warring Greek Kingdoms in the western world came the growing Roman Republic and the Iranian Parthian Empire. As a result of empires, urbanization and literary spread to locations which had previously been at the periphery of civilization as known by the large empires. Upon the turn of the millennium the independence of tribal peoples and smaller kingdoms were threatened by more advanced states. Empires were not just remarkable for their territorial size but for their administration and the dissemination of culture and trade, in this way the influence of empires often extended far beyond their national boundaries. Trade routes expanded by land and sea and allowed for flow of goods between distant regions even in the absence of communication. Distant nations such as Imperial Rome and the Chinese Han Dynasty rarely communicated but trade of goods did occur as evidenced by archaeological discoveries such as Roman coins in Vietnam. At this time most of the world's population inhabited only a small part of the earth's surface. Outside of civilization large geographic areas such as Siberia, Sub Saharan Africa and Australia remained sparsely populated. The New World hosted a variety of separate civilizations in the but its own trade networks were smaller due to the lack of draft animals and the wheel.