In the early days, India had a great civilization. From 3000-2000 BC, Harappa and Mohenjodaro were the great civilizations there. The actual occupants of India who lived there were the Dravidia race. The Dravidia were the indigenous people who have lived in Harrapa which was located in Punjab and North Karachi around 3000-2000 BC .
Dravidia was known to believe in politheist that is believing in multiple Gods. This can be segregated into many for instance, God in fertility and God in prosperity . According to Ernest Mackay in his book titled Early Indus Civilizations, most of the Indus worshipped animals such as crocodiles and elephants and trees like peepal . Moreover, rituals such as slaughtering animals were held to be presented in front oftheir Gods. Apart from that, they found a man-made pool where a ritual called “Great Bath” was performed. The “Great Bath” was the holy bath ritual and this was found in Mohenjodaro. The purpose of this worship and ritual was to show their gratitude towards the Gods to receive blessing and prosperity upon them .
There is a famous theory interpreted as the change of the India social life structure in those days. This theory relates to Arya entering India. Around 1800-1000 BC, the Arya which was originated from Iran entered India. The word Arya means noble and they were noble race. Their facial features were fair skin with pointed nose and were famous for their art of war. The Dravidia were not good in war and therefore they were defeated by the Arya. Hence, the Dravidia people migrated to the South part of India . The evidence of this war was proven by the archaeologist who performed the excavation in Harappa. They found lots of dead human skeleton which proves that the war happened between Arya and Dravidia and Arya defeated Dravidia. Apart from that, the Harappa city was demolished .
Introduction of Monotheism By Arya to India
In India, the structure of the religion was influenced by the Arya until Brahma was introduced or also known as Hindu today. Way before Arya entered India, they had their own belief and it was called Arya Dharma . Dharma means ‘Way of Life’ and therefore Arya Dharma means ‘Arya Way of Life’. The concept of Arya Dharma is that they believe in one God and this is referring to the monotheism . Most of the westerner researchers claimed that Arya Dharma was influenced by the Zoroaster religion which was originated from Iran. This is because there are similarities in the Book of Veda and the Holy Book of Zoroaster that is the Gathas according to Mary Boyce in her research from the Zoroastrians: Their Religious Beliefs and Practices.
Another source claims that Arya Dharma was influenced by the Abraham or Ibrahim from Mesopotamia. Prof Uthaya Naidu mentioned in his book titled “Bible of Aryan Invasions: Aryan Invasions & Genocide of Negroes, Semites & Mongols The Bible of Aryan Invasions” that in between 1500 BC and 800 BC there were 4 attacks following by the Aryan entering India. The 4 attacks were called:
1. Arya Rigvedic (1500 BC)
2. Aryan II (1400 BC)
3. Ras Arya Krishnaite (1200 BC)
4. Ras Arya Mahabharata (900-800 BC)
The first invasion which is known as Arya Rigvedic was the major attack caused by Arya to India and fought with Dravidia which was the first people to attack the civilization in Indus river. It resulted in Dravidia was defeated and were expelled to South India. In the following century which was known as the second entry of Arya to India it was known as Indo-Arya civilization. The Arya conquered two main parts in India: Punjab and Doab . After the entrance of Aryan II to India, the Book of Veda was written in Sanskrit as the main language. This is because the Aryan II spread their belief and religion to India. The belief and religion that was brought to India by Arya was influenced by monotheism.
They worshipped a God named Brahman. Apart from that, they also believed in multiple Gods that represents world such as Pretivi as the God of Earth, Surya as the God of Sun, Vayu as the God of Wind, Varuna as the God of Ocean and Agni as the God of Fire . Although the names of the Gods had only existed after the writing of Book of Veda, the spiritual belief towards the Gods were there way before that .
When Aryan started to migrate to India, the mixture of the culture and religion occurred and therefore this was how the Book of Veda was written around 1400 to 1000 BC. It was known as the Vedic Era . The Book of Rig Veda, Sama Veda, Yajur Veda and Athraya Veda were written based on the mixture of Arya theology and Dravidia. Moreover, they had also written another Holy book which was called Upanishads. The content of Books of Veda and Upanishads were combined and called as the Holy Book of Sruti was revealed .
Veda was originally called as Brahma religion and the language of this religion was called the Sanskrit. The believers mastered this language . Originally, the Sanskrit was mastered by the Aryan only. But after mastering the language, the people were slowly not interested to master the language anymore. Hence, the mixture of the Sanskrit language with the language used by Dravidia, came in the new languages such as the Kannada, Telugu and Malayali. These new languages were originated from the ancient language of Proto Dravida which was mixed from the halt of the usage of the Sanskrit by the Brahmin .
This is because the Brahmin or the priests of the Brahmin were originally from the Arya clan and therefore, they were responsible to teach the Indians in Sanskrit language .
The Birth of Non-Caste Religion in India
In the 7th Century BC, the Brahmin had introduced the caste system that is the hierarchical system . This hierarchical system consisting of religionist, rulers (government), companies and those people who followed the religion. In 600 BC, a ruler for the Jainism religion came into picture and was known as Vardhmana or Mahavira. This religion did not practice the caste system like the Brahma did. The language used in Jainism was Prakrit but this religion was only practiced inside India. No sign of development of this religion outside India.
After a few years later, around 563 BC, the Siddharta Gautama Buddha was born. He introduced his religion which was called Buddha without the caste system. He used Pali as the langugage to convey the religion. He had so many students under him and this made the Buddhism to be spread world wide. When these two religions (Jainism and Buddhism) were developing, the Vedic or the Brahma was slowly degenerating.
The Introduction to the writing of Holy Book of Smriti
As the time, culture and geography changed, the Sanskrit language had diminished. But the effort was still there to make sure that the Sanskrit language preserved. Wendy Doniger mentioned in her book titled The Hindus: An Alternative History that a new wave existed which had historical and saga elements and these books are Mahabhrata and Ramayana. The writing of these scriptures started in 300 BC-200 C and some historians claimed that the writing of the two books started in 400 BC .
This time around was known as the Wiracarita where a big epic war occurred between Arjuna, Krishna (Mahabhrata) and Sri Rama (Ramayana). In Mahabhrata, it consists of stories that relates to the existence of multiple Gods that led to the development of the Book of Purana . The writing and the development of this Book was meant to maintain the usage of Sanskrit language among the Aryan people in India.
During 300 BC till 500 C was the time of new development in Brahma. It was known as Puranic time where the writing of the other scriptures began besides the Book of Sruti (Veda and Upanishads) in order to be used in Brahma . The writing of the other Holy Book besides Sruti was known as the writing of Smriti. Among the Holy Books that were written during this time comprising Books of Sutra Dharma, Shastras, Mahabhrata, Ramayana, Bhagavad Gita, Pura and others.
During Puranic time, the construction of the statue of Greece or Hellenism had started to enter India and influenced the Brahma. Apart from that, Dravidia was the main religion that introduced polytheism and it also reflect in the writings of the holy books and Purana story-line. In the early history, the Brahma was not known as worshipperof multiple Gods (polytheism). They only believed in one God. Around 1500 BC to 300 BC (Vedic), no signs of holy statues found and worshipped by the people during that time.
Why the era of Vedic do not have statue?
In the era of vedic (1500 SM- 500 SM), there were no idol or image of God worshipped by the people during that time. It is due to the law which forbid to create idols in the image of God as stated in the book of Veda and Upanishads (Sruti). Furthermore, the book Veda and Upanishads should be their reference. Following verse shows the prohibition of worshipping idols:
1) “na tasya pratima asti
“God do not have any image.” (Yajurveda 32:3)
2) “shudhama poapvidham”
“God do not have established body and it is pure.” (Yajurveda 40:8)
3) “Andhatama pravishanti ye asambhuti mupaste”
“Those worshipper of nature (air, water, fire or soil) will enter darkness and even goes in deeper for those who worship idols.(Yajurveda 40:9)
Even during this era, the characteristics of monotheism of God was emphasized in the Rig Veda and Upanishads.
1) “Ekam sadvipra bahudhaavadanti
“God is one and intelligent people praise God with various name” ( Rigveda book 1: hymn 164 verse 46)
2) “Ekam eva advityam Brahman”
“God is one, there is no two” (Chandogya Upanishad chapter 6 hymn 2 verse 1)
Moreover, there are many verses similar to it but the religion started to grow with the additional Holy Book in year of 300 SM. It is known as the wave writing of the Smriti Book which gave an impact towards Brahma religion till the story of God’s and King’s that rapidly persuaded by own verse interpretations. It can be seen in the book of Mahabhrata and the book of Purana. The book of Purana contained many parts which well known as Mahapurana which divided into 18 books such as;
a) Brahmapurana, b) Padmapurana, c) Visnupurana, d) Bhagavatapurana, e) Naradapurana, f) Markandeypurana, g) Agnipurana, h) Bhavisyapurana, i) Brahmavaiavartapurana, j) Lingapurana, k) Varahapurana, l) Skandapurana, m) Kurmapurana, n) Matsyapurana, o) Garudapurana, dan p) Brahmandapurana.
This book was gathered within a long duration and known as the written period of Puranic.  There were mixed and additional information with regards to the question of God in Brahma religion happened in this era. It started from this era which the doctrine of pantheism and polytheism started to expand and grow within the Brahma adherent. The doctrine which believed that everything are able to provide benefits which constituted the elements of God (pantheism), worshipping idols and make God more than one which align with the incarnation of God. It undergo through creature body with various types (avatar) and henotheism.
New command of inventing Idols
The book Purana encourage the Hindu adherent to invent idols. There are text in the book Matsya Purana which explained about it and located under the topic of Arsetektur (base on the reference of I Wayan Maswinara.
“There are idols that must be placed inside the temple. The idol of God Visnu need to be designed with four hands and eight hands. If the design consist of 8 hands, the hand, we must hold the Sankha (Skin of a shell), gada, arrow and lotus. Left hand need to hold the arc, Padma, and a cakra. If they invent only four hands, gada and Padma consist in my right hand while cakra and sankha will be on left hand. Visnu will be pictured by standing on the early. Garuda the king of bird will move around it. Then, Garuda will be at the right leg of Visnu. Idols of Laksmi Goddess will be on the left side of Visnu idols and Laksmi idols need to hold the Lotus flower. The good idols will be created by gold, silver, copper, jewelry, stone, wood and a mix of metal. The size of Gods and Goddess has to be true.”
Same goes to other Gods. Purana has outlined the picture and image of their God until the idols needs to be created. For example, the face and structure of Siva has been outlined in the Purana:
”Idol of Lord Siva need to be created using a loose long hair and need to put a moon on the forehead. The idols need to describe Siva at the age of 16 years old. Siva need to wear clothes which created by animal fur and has snake necklace on his neck. The ear will be attach with peacock fur. If the stick need to be attached, it has to be on the left side. Furthermore, Siva ride on a cow which the idols have two hands and if the idols of Siva is made in situation of dancing, the idols need to consist of 10 hands. Moreover, if the idols is meant to show Lord Siva destroying the Tripura, the idols need to have 16 hands.”
The book of Purana explained the story about the requirement of designing the Idols. It shows the development which do not belongs to the actual teaching of Veda. Even Siva did not mention in the earliest book such as Veda and Upanishads.  In the Era in which is the rising of second Hindu religion which there were many additional doctrine of the Veda teaching.
In the era of Puranic, the religion of Hindu was influenced by polytheism. Besides, the development and expanding of worshipping the idols at temples happened. After that, the religion of Brahma started to extinct. During the rulings time of Asoka in India, under the empire of Maurya. King Asoka declared the Buddhism as their official religion. In year 269-232 SM. King Asoka emphasized on the language usage of Pali in order to spread the religion of Buddha. 
At the ruling time of Asoka, the development and preaching of Hinduism in India was stunted due to expanding of Buddhism religion rapidly towards the east. After a while, Brahma religion gain new opportunity when the empire of Gupta took over the ruling dominantly in India.
During this era, the usage of Sanskrit language was revived and indicates Hinduism religion as an official religion. Moreover, during the rising of Gupta empire (320 M- 500 M) shows the development of Hinduism traditions which is to create few flow that focuses towards the Lords inside the community. For example, Vaishnavisme ( focused on Vishnu), Shaivisme ( focused on Siva ) and Shaktisme ( focused on head of Goddess). That’s the reason why the Hindu temple was influenced by God from Siva, Vishnu and Devi family. There was no temples focus on Brahma result to different types of Brahma which rarely spoken by the Hindu followers.
Based on Wendy Doniger books entitle The Hindus, the written of Smriti book was successfully completed and gathered during the Gupta empire and was made as reference for Hindu followers. The books of Purana was made as an important reference of the infrastructure of idols inside the temples. The image of Gods inside the temples was majoritydesigned according to the book of Purana. Therefore, the practice of Hinduism in this era are mostly influenced with the development of Puranic and Gupta empire.
Discussion about the Hinduism name
The word Hindu or Hinduism was not found in any holy book of Hinduism even the word was been newly introduced. Based on Pundit Jawahar LaI Nehru inside the book, Discovery of India, the word Hindu was firstly used by the Persian which refers to the Indus River. They called it as Hindus.
After that, the word Hindu was used by an author from British in the year of 1830. It refers to the teachings and religion professed by the community overthere. Polemic occurred among the scholars in India towards the name of religion professed by the Hindu follower. They embraced the Veda scriptures. They enjoyed with the name Vedanta which means a person who followed the Veda scripture. There is also other name such as Sanatana Dharma which means the eternal truth (natural law). They are also synonym with Brahma religion while the word Hindu do not agree whole among their scholar. Moreover, the word was expand and become a specific name towards the religion embraced by a group of people who follow the Veda scriptures and culture of India.
The original teaching of Veda and Upanishads is emphasized on the concept of monotheism. The concept of God and Goddess was changed whilst entering the era when smriti is written. After that, it developed and expanded through the introduction of types of worshipping according to the classes of their Gods such as Siva, Vishnu and Dewi. It continued till the era which the Hinduism owns the history and faced the up and down phased in a long duration. It also includes the Modern era which consist of few figures such as Ram Mohan Roy, Sri Ramakrishna, Swami Vivekananda, Mahatma Gandhi and many more that contribute the innovation of ideas towards this teaching.