The history of Asia can be seen as the collective history of several distinct peripheral coastal regions such as, East Asia, South Asia, and the Middle East linked by the interior mass of the Eurasian steppe.
The coastal periphery was the home to some of the world's earliest known civilizations, with each of the three regions developing early civilizations around fertile river valleys. These valleys were fertile because the soil there was rich and could bear lots of root crops. The civilizations in Mesopotamia, the Indus Valley, and China shared many similarities and likely exchanged technologies and ideas such as mathematics and the wheel. Other notions such as that of writing likely developed individually in each area. Cities, states and then empires developed in these lowlands.
The steppe region had long been inhabited by mounted nomads, and from the central steppes they could reach all areas of the Asian continent. The northern part of the continent, covering much of Siberia was also inaccessible to the steppe nomads due to the dense forests and the tundra. These areas in Siberia were very sparsely populated.