According to this theory, India was conquered by a nomadic tribe of Indo-European tribes from Central Asia around 1500 to 100BC. It is believed that these fair skin nomads fought a huge battle with the dark skinned 'Dravidian Civilization', from which they took most of what later became the Hindu culture. The Aryan Invasion theory is based on the ruins that were discovered in the Indus Valley.
According to the historians. Aryans came to India around the time of 1500 BC, since the Indus Valley culture was earlier than this they had to conclude that the Indus Valley Civilization was pre Aryan. It was also stated by these same scholars, that the Vedic culture originated from primitive nomads in Central Asia. The vedic culture was thus said to be warriors of central Asian decent who came into India with horse drawn charriots and iron weapons but no charriot was ever discovered in Indus Valley sites. Thus the whole idea of Nomads with charriots has been challenged. The question arrises how could these nomads travel through rough mountain valleys ( in tough weather)with these charriots? Therefore it can be said that metals and wheel fragments that were discovered could come from the vedic culture. Opponents of the theory , point to many different flaws in the theory.
The theory of Aryan invasion divided India into Northern Aryan and Southern Dravidian culture, which were hostile to each other. This theory also gave the Britishers an excuse in conquest of India. They could claim to only be doing what their Aryan ancestors had previously done. Lastly by implementing the Aryan Invasion theory, the history and science of India was given mostly a Greek basis, therby discarding the vedic culture and history. The Rig Veda scripture describes Hindu Gods as 'destroyers of cities'. This was also in regard to Vedic as primitive and non urban culture that destroys cities and urban civilizations.
however according to Dr David Frawley, a Vedic scholar , there are many versions of 'Rig Veda' that speak of Aryans having their cities of own. He points out that the destruction of cities does not does not simply turn these people into nomads.
Therefore, the idea of vedic cultures destroying but not building the cities is baseed upon ignoring what the Vedas actually say about their cities. Many later excavations had shown that the Indus Valley Civilization was not destroyed by foreign invasion but by a force of nature, like earthquake or flood. Most recently there have been discoveries of new cities in the Indus valley. This may eliminate the what we call as the dark age, that followed the pre-Aryan invasion and " shows a continuous urban occupation in India , back to the begining of the Indus culture." In regards to the war between the light and dark civilizations, it amy be looked at in the light that the Vedic civilization was the civilization of the God or the sun, therefore they were light skinned civilization.
The theory of Aryan invasion is a very interesting theory that has been intriguing researchers. The acceptance of the Aryan Invasion Theory was the easiest way for Aryan race to implement their dominance of the world. In contrast declining it would make Ancient India one of the oldest , largest and the most central of ancient cultures. It would also fortify that the Veda would be the most authentic record of the ancient world. Most importanly it would affirm the Hindu tradition that the Dravidians were the early offshoots of the vedic people.