Krishna in Mahabharata taught us worldly powers
Krishna was the key political figure in overthrowing 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.
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 Yudhishthira 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.