The kingdom of Anga is mentioned in the Atharva Veda and was located roughly at the site of the present day Bihar and some parts of West Bengal. On the north was River Ganga and it was separated from the Magadha by River Champa. Anga was one of the most flourishing cities and was an important center of trade and commerce. It was regarded as one of the six principal cities of early India.
Assaka / Ashmaka
Avanti was a very important kingdom located in Western India and was considered to be one of the four important monarchies during the time Buddhism began in India. River Vetravati used to flow right through Avanti thus dividing it into north and south provinces. Avanti was located roughly at the place where the state of Madhya Pradesh is located now. Avanti was an important center of Buddhism and later became a part of Magadhan Empire.
Chedi / Cheti
There were two different settlements of the Chedis, also known as Cheti. One was in the mountainous regions of Nepal while the other was located near River Yamuna. The southern boundaries of Chedi went till the banks of River Narmada. The Chedis are mentioned in Rig Veda, which is regarded as the oldest scripture. This means that Chedis were prevalent here since a long time.
The Gandharas established themselves since the Vedic Age on the banks of River Kubha till the River Indus. With time, they crossed Indus and expanded their territory into Punjab. The Gandharas were very aggressive in nature and were masters of the art of warfare. It is said that this kingdom was founded by the son of Aruddha known as Gandhara.
Kamboja was said to have been located on either sides of the Hindukush. In early scriptures and literature, Kamboja is mentioned along with Gandhara, Darada and the Bahlika quite a number of times. The Kambojas were supposed to have both Indian and Iranian similarities.
The Aryans who had settled around Varanasi were known as Kasis. The city was flanked by the rivers Varuna and Asi from which the place derives its name. Kasi was the most powerful kingdom of the sixteen Janapadas before the rise of Buddhism. During the rise of Buddha, it was converted into Kosala. This place is mentioned as Kausika / Kausaka in the Matsya Purana.
Kosala was located around 70 miles to the north west of present day Gorakhpur in Uttar Pradesh. It was flanked in the south by River Ganga, in the north by the Himalayas and in the east by the River Gandak. The ruler was called king Prasenjit who was succeeded by his son Vidudabha. During his son's reign, Kosala was combined with Magadha. The three chief cities of Kosala were Ayodhya, Saketa and Sravasti.
The origin of the Kuru clan can be traced to the Puru - Bharata family. Some of them were settled in central India and some were living beyond the Himalayan ranges. It is said that the founder of Kururashtra in Kurukshetra was the son of Samvarsana called Kuru. The Kurus were known for their profound wisdom and sound health. The Kurus switched to republic form of government from monarchy during 5th Century B.C.
Machcha / Matsya
The kingdom of Matsya or Machcha is said to have comprised the region of the present day Jaipur in Rajasthan along with Alwar and Bharatpur. The founder of this kingdom was king Virata and the capital of this kingdom was named Viratanagara after him. The Matsya once formed a part of the Chedi kingdom as there are evidences that show that this place was ruled by the king of Chedi.
The Magadhas are referred to in the Atharva Veda. According to the early scriptures, the Magadhas were not fully Brahmins. Thus, they were loathed at and were spoken of in contempt. Except for King Pramaganda, no other ruler is mentioned in the Vedas. It is stated in the Mahabharata that Magadha came into the limelight under the king Bimbisara and later under his son Ajatasatru. It was one of the chief empires of India during those times. The kingdom of Magadha was situated roughly where the present day Bihar is located.
Most of the scriptures of the Jains and Buddhists mention the Mallas. Their tribe was supposed to be quite powerful and they lived somewhere towards the Eastern India. The Mallas had a republic form of society and their dominant territory comprised of nine provinces. Two of these nine provinces (Pava and Kusinara) gained much importance in due course of time when Buddha came over here and took his last meal before breathing his last at Kusinara.
The Panchalas were located in the north of India and had their province to the east of the Kurus. They were located between the Himalayan ranges and river Ganga. One can say that it was located roughly at the place where the modern day Uttar Pradesh is located. The Panchalas were originally monarchial in nature and later transformed to the republican form of government during the 5th Century B.C. They are mentioned in Kautilya's Arthashastra as following the constitution of the king.
The location of the Surasena was around the west side of river Yamuna and had its capital city at Mathura. The king of Surasena, Avantiputra played a vital role in promoting Buddhism in his kingdom. He was one of the chief disciples of Buddha and aimed at spreading his knowledge and wisdom all through his kingdom. The capital city of Mathura was an important center for the worship of Lord Krishna. With time, the kingdom of Surasena was annexed by Magadha Empire.
Vajji / Vriji
The Vajji or Vriji comprised of eight to nine allied races and this kingdom became an important center of cultural and political activities. It was essentially located in northern India. Out of the nine races, the Licchhavis, the Vedehans, the Jnatrikas and the Vajjis were the most important. The Licchhavis were an independent clan and their capital was called Vaishali. It was an important center of Buddhism and the headquarters of the powerful republic of Vajjis. Buddha is supposed to have visited Licchhavis on many occasions. As time passed, the kingdom of Licchhavis was conquered by the king of Magadha, Ajatasatru.
Vamsa / Vatsa
Considered to be an offshoot of the Kurus, the kingdom of Vatsa or Vamsa was roughly situated at the location of modern day Allahabad in Uttar Pradesh. The capital city was known as Kaushambi, which was a prosperous city. A number of rich merchants dwelled here. It was an important gateway for goods and people coming from the North West and south. The ruler of Vatsa was known as Udyana and he was a very powerful ruler. He became a follower of Buddha and adopted Buddhism as the religion for his kingdom.