In the later Vedic Age, a number of small kingdoms or city states, dominated Magadha. Many of these states have been mentioned during in Buddhist and Jain literature as far back as 1000 BCE. By 500 BCE, sixteen monarchies and ‘republics’ known as the Mahajanapadas—Kasi, Kosala, Anga, Magadha, Vajji (or Vriji), Malla, Chedi, Vatsa (or Vamsa), Kuru, Panchala, Machcha (or Matsya), Surasena, Assaka, Avanti, Gandhara, Kamboja—stretched across the Indo-Gangetic plains from modern-day Afghanistan to Bengal and Maharastra. Anga and Magadha is the modern North Bihar and South Bihar respestively.
The first reference to the Angas is found in the Atharva-Veda where they find mention along with the Magadhas, Gandharis and the Mujavats apparently as a despised people. The Jaina Prajnapana ranks Angas and Vangas in the first group of Aryan people. Based on Mahabharata evidence, the country of Anga roughly corresponded to the region of Bhagalpur and Munger in Bihar and parts of Bengal. River Champa formed the boundaries between the Magadha in the west and Anga in the east. Anga was bounded by river Ganga on the north. Its capital Champa, formerly known as Malini, was located on the right bank of river Ganga, near its junction with river Champa. It was one of the very flourishing cities and is referred to as one of six principal cities of ancient India (Digha Nikaya). It was also a great center of trade and commerce and its merchants regularly sailed to distant Suvarnabhumi. Anga was annexed by Magadha in the time of Bimbisara.
The first reference to the Magadhas occurs in the Atharva-Veda where they are found listed along with the Angas, Gandharis and the Mujavats as a despised people. The bards of Magadha are, however, referred to in early Vedic literature and are spoken of in terms of contempt.
Rigveda mentions a king Pramaganda as a ruler of Kikata. Yasaka declares that Kikata was a non-Aryan country. Later literature refers to Kikata as synonym of Magadha.
With the exception of the Rigvedic Pramaganda, whose connection with Magadha is very speculative, no other king of Magadha is mentioned in Vedic literature. According to the Mahabharata and the Puranas, the earliest ruling dynasty of Magadha was founded by king Brihadratha, but Magadha came into prominence only under king Bimbisara and his son Ajatasatru. In the war of supremacy which went on for long between the nations of Majjhimadesa, kingdom of Magadha finally emerged victorious and became a predominant empire in Mid India.
The kingdom of the Magadhas roughly corresponded to the modern districts of Patna and Gaya in southern Bihar, and parts of Bengal in the east. It was bounded on the north by river Ganga, on the east by the river Champa, on the south by Vindhya mountains and on the west by river Sona. During Buddha’s time, its boundaries included Anga. Its earliest capital was Girivraja or Rajagriha modern Rajgir in Patna district of Bihar. The other names for the city were Magadhapura, Brihadrathapura, Vasumati, Kushagrapura and Bimbisarapuri. It was an active center of Jainism in ancient times. The first Buddhist Council was held in Rajagriha in the Vaibhara Hills. Later on, Pataliputra became the capital of Magadha.
Many of the sixteen kingdoms had coalesced to four major ones by 500/400 BCE, that is by the time of Siddhartha Gautama. These four were Vatsa, Avanti, Kosala and Magadha.
In 537 BCE, Siddhartha Gautama attained the state of “enlightenment” in Bodh Gaya, Bihar. Around the same time, Mahavira who was born in a place called Kshatriyastan in the ancient kingdom of Lachuar in Jamui District in modern day Bihar. He was the 24th Jain Tirthankara, propagated a similar theology, that was to later become Jainism. However, Jain orthodoxy believes it predates all known time. The Vedas are believed to have documented a few Jain Tirthankars, and an ascetic order similar to the sramana movement. The Buddha’s teachings and Jainism had doctrines inclined toward asceticism, and were preached in Prakrit, which helped them gain acceptance amongst the masses. They have profoundly influenced practices that Hinduism and Indian spiritual orders are associated with namely, vegetarianism, prohibition of animal slaughter and ahimsa (non-violence).
While the geographic impact of Jainism was limited to India, Buddhist nuns and monks eventually spread the teachings of Buddha to Central Asia, East Asia, Tibet, Sri Lanka and South East Asia. Nalanda University and Vikramshila University one of the oldest residential universities were established in Bihar during this period.
According to both Buddhist texts and Jain texts, one of Pradyota tradition was that king’s son would kill his father to become the successor. During this time, it is reported that there was high crimes in Magadha. The people rose up and elected Shishunaga to become the new king, who destroyed the power of the Pradyotas and created the Shishunaga dynasty.
Source : Wikepedia