The Vedic Period

As we know, the Indus Valley Civilisation, which is now in modern-day Pakistan and northwest India, then in the third millennium BCE and then in the second millennium BCE starts its decline. We still don't know why it declined. Maybe due to a natural disaster, maybe a river that was vital to them or maybe climate change. We still don't know. 

The Vedic period was the era of the Indo-Aryans in South Asia, who migrated into the Indus Valley during its decline.
We get the name Vedic from the literary works called the Vedas, which is a Sanskrit word meaning knowledge. These Vedic people are the baseline of modern Indian culture. 

The important Vedas are the Rigveda, Yajurveda, Samaveda, and Atharvaveda, with Rigveda being the oldest of the group. Rigveda first appeared at the start of the Vedic period, around 1500 BCE, and it continued until around 1200 BCE, which is around 3,000 - 3,500 years ago.

They were cattle herders, and they may have been nomadic and were expanding beyond the Indus River Valley, to the whole of what is now the Gangetic plain in north-east India and Bangladesh. 
They did become farmers around what is the late Vedic period and started becoming more like a kingdom.

Then, the Hindu stories or Epics of Mahabharata and Ramayana, these stories or poems were originally told verbally, but maybe during this late period or after the Vedic period, these stories would eventually be written down.

Sanskrit is one of the oldest Indo-European languages on earth, and it is related to languages like Greek and Latin, and some Germanic languages like Danish, Norwegian and Swedish. Sanskrit is as old as Mycenaean Greek and the Hittite Language.

The first documented piece of the Indus Valley Civilisation is from the Vedas, and they had a word which is Sindhu, which may  have been mispronounced and misspelt to the point that it may have turned into the word Hindu, then the word Indus may have turned into the word India.

There were also social structures and classes, named the Varnas, such as the Brahmins which are the teachers, scolars and the priests, the Kshatriyas which are the kings and the warriors, Vaishyas which are the farmers, merchants and the artisans and finally the Shudas which are the labourers.