Krishna was the key political figure, in overthrowing Kamsa or Kansa, the king of Surasena Kingdom. The kingdom of Surasena was the native kingdom of Yadava clans constituted by the Andhakas, Vrishnis and Bhojas. By overthrowing Kansa, Krishna re-established the old king Ugrasena on the throne and stabilized the kingdom, from collapse due to factional fighting within the kingdom.
The next threat came from outside the country, from the Magadha Kingdom. The ruler of Magadha, Jarasandha, attacked Surasena many times and weakened its military. Krishna and other Yadava chief tried all their best to hold on. At last they had to flee from their native kingdom to the south and to the west.
Later, with the initiative of Krishna, the Yadavas who fled from Surasena formed a new kingdom called Dwaraka. Its capital was Dwaravati a city well protected by mountains on all sides, in an island, not far from the Gujarat coast. This made it immune to attacks from land. The kingdom prospered by sea trade, with sea-faring kingdoms.
Krishna also established a tie-up of Yadavas with the Pandavas, a faction of Kurus, who were fighting against the established Kuru Kingdom. This tie up also benefited the Yadavas, strategically. With the help of the Pandavas they overthrew the Magadha king Jarasandha who was their biggest enemy. For this assistance, Krishna in turn helped the Pandavas to win the Kurukshetra War against the Kurus headed by Duryodhana. Thus the rule of the Pandava Yudhisthira was re-established by Krishna at Indraprastha, the modern-day (Delhi).
However, The Yadava chiefs fought the Kurukshetra War, on both sides, and even after the war ended, the enmity among the Yadava leaders continued. After 36 years, since the Kurukshetra War, another war broke among the Yadavas, in their own kingdom. This resulted in the absolute destruction of the Yadava kingdom in Dwaraka, with Balarama and Krishna also departing due to grief. This fight among Yadava is also attributed to curse from Gandhari, mother of Duryodhana to Krishna.
But the help Krishna extended to the Pandava Yudhisthira, paid off. When the rule of Yudhisthira ended, he established the Yadava prince Vajra on the throne of Indraprashta along with the Kuru prince Parikshit, at Hastinapura. Thus the royal lineage of the Yadavas continued through the prince Vajra. Parikshita was son of Abhimanyu, grandson to Vasudeva and Vajra great-grandson of Vasudeva was also grandson to Yudhisthara, son of Draupadi's daughter Sutanu and Asva, Krishna 's son by Jambavati. Similarly, Satyaki's daughter 's son Bhuti who was grandson of Bhima and founder of Malavas was made king of Saraswat nagar. Krishna and Rukmini 's daughter was married to Bali, son of Kritvarma, whose son Andhaka got Mrittivakata. Bali was nephew to Yudhisthara and Duryodhana, married to their sister. Another son of Jambavati, Samba 's son, cousin to these three founded Moolsthana or Multana. Pradyumana, Krishna 's son, Krishna 's brother Gada and Samba had married three daughters of Vajranabha and shared his kingdom. What is the source for the reference to Draupadi's daughter and Satyaki's daughter's son as grandson of Bhima and Rukmini's daughter marrying Kritavarma's son who also married Duryodhana's sister? Late Sri. Kulapati K.M.Munshi's famous narration of the life of Lord Krishna, Krishnavatara (Volumes 1 to 8) published by Bharatiya Vidya Bhavan is a very good read into the political aspects of Lord Krishna, painting Krishna not as the God Almighty but as a human Hero and a Great Leader. A very interesting read between the lines into the inner aspects of politics by Krishna as a human being.
The following sections shows glimpses of Krishna's political life, as a supporter of the Pandava cause, and as a mediator among his own kinsmen.
(Mahabharata, Book 1, Chapter 223) Even this is my opinion: go ye cheerfully after Dhananjaya and by conciliation stop him and bring him back. If Partha goes to his city after having vanquished us by force, our fame will be gone. There is no disgrace, however, in conciliation.
He also conquered Bana or Vana of Sonitapura (Sonitpur of Assam), to the east of Prakjyotisha. However they became allies, as Krishna's grandson Aniruddha married Usha, the daughter of Bana. He belonged to the Daitya clan of Asuras.
In (Mahabharata, Book 5, Chapter 62), Krishna is described as the slayer of Vana and Bhumi’s son (Naraka)
(Mahabharata, Book 5, Chapter 130) He hath slain Jarasandha, and Vakra, and Sisupala of mighty energy, and Vana in battle, and numerous other kings also have been slain by him. Of immeasurable might, he vanquished king Varuna and also Pavaka and Indra and Madhu and Kaitabha and Hayagriva)
(Mahabharata, Book 5, Chapter 48)...that Vaasudeva (Krishna), viz., who having mowed down in battle by main force all the royal warriors of the Bhoja race, had carried off on a single car Rukmini of great fame for making her his wife.
(Mahabharata, Book 7, Chapter 11) Krishna, vanquishing all the kings at a self-choice, bore away the daughter of the king of the Gandharas. Those angry kings, as if they were horses by birth, were yoked unto his nuptial car and were lacerated with the whip. The contest at swyamvara was chaining a set of bulls to plough.
(Mahabharata, Book 7, Chapter 23) The Pandya King Sarangadhwaja's country having been invaded and his kinsmen having fled, his father had been slain by Krishna in battle. Obtaining weapons then from Bhishma and Drona, Rama and Kripa, prince Sarangadhwaja became, in weapons, the equal of Rukmi and Karna and Arjuna and Achyuta. He then desired to destroy the city of Dwaraka and subjugate the whole world. Wise friends, however, from desire of doing him good, counselled him against that course. Giving up all thoughts of revenge, he ruled his own dominions.
Krishna's philosophical conversation with his friend and cousin Arjuna during the Kurukshetra War later became known as the famous Bhagavad Gita, the holy book of Hindus. How he amassed this great knowledge is revealed in the Anu-gita chapters of Mahabharata, which states that he got this knowledge by interactions with many learned men, and by his own meditations.
(Mahabharata, Book 14, Chapter 16) On one occasion, a Brahmana came to us. Of irresistible energy, he came from the regions of the Grandsire. He was duly reverenced by us. Listen, to what he, said, in answer to our enquiries. The Brahmana said, That which thou askest me, O Krishna, connected with the religion of Moksha (Emancipation), led by thy compassion for all creatures and not for thy own good,--that, indeed, which destroys all delusion, O thou that art possessed of supreme puissance I shall now tell thee duly. Do thou listen with concentrated attention as I discourse to thee.
(Mahabharata, Book 6, Chapter 26) As a man, casting off robes that are worn out, putteth on others that are new, so the Embodied (soul), casting off bodies that are worn out, entereth other bodies that are new. Weapons cleave it not, fire consumeth it not; the waters do not drench it, nor doth the wind waste it. It is incapable of being cut, burnt, drenched, or dried up. It is unchangeable, all-pervading, stable, firm, and eternal. It is said to be imperceivable, inconceivable and unchangeable.
(Mahabharata, Book 6, Chapter 26) All beings (before birth) were unmanifest. Only during an interval (between birth and death), O Bharata, are they manifest; and then again, when death comes, they become (once more) unmanifest.
(Mahabharata, Book 6, Chapter 27) In this world, two kinds of devotion; that of the Sankhyas through knowledge and that of the yogins through work.
(Mahabharata, Book 6, Chapter 29) Arjuna said,--Thou applaudest, O Krishna, the abandonment of actions, and again the application (to them). Tell me definitely which one of these two is superior. The Holy One said—Both abandonment of actions and application to actions lead to emancipation. But of these, application to action is superior to abandonment. He should always be known to be an ascetic who hath no aversion nor desire. For, being free from pairs of opposites, he is easily released from the bonds of action.
(Mahabharata, Book 6, Chapter 29) He who is wise never taketh pleasure in these that have a beginning and an end.
The cult of Krishna Vasudeva (IAST "Krishna, son of Vasudeva") is historically one of the earliest forms of worship in Krishnaism and Vaishnavism. This tradition is considered separately to other traditions that led to amalgamation at a later stage of the historical development, that form the basis of current tradition of monotheistic religion of Krishna. Some early scholars would equate it with Bhagavatism, and the founder of this religious tradition is believed to be Krishna, who is the son of Vasudeva, thus his name is Vāsudeva, and according to them his followers called themselves Bhagavatas and this religion had formed by the 2nd century BC (the time of Patanjali), or as early as the 4th century BC according to evidence of Panini and that of Megasthenes and in the Arthasastra of Kautilya, when Vāsudeva was worshiped as supreme Deity in a strongly monotheistic format, where the supreme Being was perfect, eternal and full of grace. In many sources outside of the cult, devotee or bhakta is defined as Vāsudevaka. Harivamsa, a later addition to Mahabharata as well as Bhagavata purana speak about his childhood in the village of Vrindavana, where Krishna passed his childhood and teenage days.