About 1500 BC, India was invaded by Indo-European people. These people came from the area between the Black Sea and the Caspian sea. Between 2500 and 2000 BC, many Indo-Europeans migrated all over Eurasia. Some went to Europe and became the Romans and the Greeks, some settled in Turkey and became the Hittites. Others migrated south-east instead. Some of them stopped in Iran, while others continued south-east to Pakistan and India. The slow migration did not arrive in northern India until about 1500 BC. In India, the Indo-Europeans are usually called the Aryans.
Some people have disputed this arrival of the Indo-Europeans, and if
you search the web you will find some sites saying that it never happened.
But there are written records of the language that these Indo-European
people brought with them to India, Sanskrit.
We can read Sanskrit, and we can easily see that many words in Sanskrit
are basically the same as in other Indo-European languages. In addition,
recent genetic evidence supports the arrival of the Indo-Europeans.
In addition to their language, the Aryans brought their gods with them to India. These gods form the basis of the Rig Veda and other sagas which were first written down in Sanskrit. They also brought the domesticated horse.
The Aryans first settled along the Indus River, in the same place where the Harappa people had lived. They settled down and mixed with the local Indian people. They lived there from about 1500 BC to about 800 BC. It seems to be at this time that the caste system got started in India.
About 800 BC, the Aryans learned how to use iron for weapons and tools. They probably learned to work iron from the people of West Asia, the Assyrians, who had learned it from the Indo-European Hittites. Once the Aryans learned how to use iron, they used their new weapons to conquer more of India, and moved to the south and east into the Ganges river valley. They settled there not long after 800 BC.
Learn by Doing - Find Iron at Home or A Project with Caste
To find out more about the Indo-Europeans' arrival in India, check out these books from your local library or from Amazon:
Eyewitness India, by Manini Chatterjee (2002). Written for kids.
Ancient India, by Virginia Schomp (2005). Written for middle schoolers. Very good for reports.
Indo-Aryan Controversy: Evidence and Inference in Indian History, by Edwin Bryant (2005). A scholar's discussion for other scholars of all the evidence concerning Indo-European nomads coming to India (for and against), but written for adults rather than kids.
The Aryan Debate, by Thomas Trautman (2005). Not a kids' book, but a collection of past writings about this question, designed to show why it is so political and what the problems are with the evidence.