In the beginning of the 6th century B.C., the northern India consisted of a large number of independent kingdoms. Some of them had monarchical forms of government, while some others were republics. While there was a concentration of monarchies on the Gangetic plain, the republics were scattered in the foothills of the Himalayas and in northwestern India. Some of the republics consisted of only one tribe like the Sakyas, Licchavis and Mallas.
In the republics, the power of decision in all matters of state vested with the Public Assembly which was composed of the tribal representatives or heads of families. All decisions were by a majority vote.
The Buddhist literature Anguttara Nikaya gives a list of sixteen great kingdoms called ‘Sixteen Mahajanapadas’. They were Anga, Magadha, Kasi, Kosala, Vajji, Malla, Chedi, Vatsa, Kuru, Panchala, Matsya, Surasena, Asmaka, Avanti, Gandhara and Kambhoja.
The Jain texts also contain references to the existence of sixteen kingdoms. In course of time, the small and weak kingdoms either submitted to the stronger rulers or gradually got eliminated. Finally in the mid 6th century B.C., only four kingdoms – Vatsa, Avanti, Kosala and Magadha survived.
The Vatsa kingdom was situated on the banks of the river Yamuna. Its capital was Kausambi near modern Allahabad. Its most popular ruler was Udayana. He strengthened his position by entering into matrimonial alliances with Avanti, Anga and Magadha. After his death, Vatsa was annexed to the Avanti kingdom.
The capital of Avanti was Ujjain. The most important ruler of this kingdom was Pradyota. He became powerful by marrying Vasavadatta, the daughter of Udayana. He patronized Buddhism. The successors of Pradyota were weak and later this kingdom was taken over by the rulers of Magadha.
Ayodhya was the capital of Kosala. King Prasenajit was its famous ruler. He was highly educated. His position was further strengthened by the matrimonial alliance with Magadha. His sister was married to Bimbisara and Kasi was given to her as dowry. Subsequently there was a dispute with Ajatasatru. After the end of the conflict, Prasenajit married the daughter of Bimbisara. After the death of this powerful king, Kosala became part of the Magadha.
Of all the kingdoms of north India, Magadha emerged powerful and prosperous. It became the nerve centre of political activity in north India. Magadha was endowed by nature with certain geographical and strategic advantages. These made her to rise to imperial greatness. Her strategic position between the upper and lower part of the Gangetic valley was a great advantage. It had a fertile soil. The iron ores in the hills near Rajgir and copper and iron deposits near Gaya added to its natural assets. Her location at the centre of the highways of trade of those days contributed to her wealth. Rajagriha was the capital of Magadha. During the reign of Bimbisara and Ajatasatru, the prosperity of Magadha reached its zenith.