Whenever and wherever there is decline of dharma (righteousness) and ascendance of adharma (unrighteousness), at that time I manifest Myself in visible form. For the protection of the righteous and destruction of the wicked, and for the sake of establishing dharma again, I incarnate Myself on earth ages after ages.
This is what the Lord Himself gave his word in the Bhagvat Geeta. The Lord did not ever fail to keep His words down the ages. From His heavenly abode at the Vaikuntha, He incarnated down to the earth to protect His devotees. Just like ‘the waves in an ocean,’ Lord Vishnu, the Supreme Soul and the sustainer, appeared down to the earth in different, different forms, one after another. However, His Avatar (incarnation) is considered as the God Himself incarnated on the eighth day of the new-moon fortnight (krishnapaksha) of the month of Shravana, when Lord Krishna appeared on this earth. Lord Krishna was born in the Duapar Yug, which came just before the Kal Yug.
the birth of Lord Krishna took place under bizarre conditions. Krishna is considered as an incarnation of Lord Vishnu who appears to the world to get rid of all evil demons. He was born at midnight stroke on a dark, rainy night to ‘Devaki’ and ‘Vasudev’ who was imprisoned by Devaki’s brother Kansa.
It had been prophesied that the eight son of Devaki would take the ghost out of the evil king Kansa. On hearing this prophesy, Kansa got his sister imprisoned and killed her seven children one by one but when Krishna was born, there was divine involvement to protect the life of baby Krishna. The guards had fallen into slumber and could not inform their master about the newborn child.
An echoing invisible voice powered Vasudev to carry the baby to Gokul and exchange with the newborn baby Nanda and Yashoda. The fetters and the jail gates were opened amazingly and Vasudev took the child in a tiny basket, through the waters of Yamuna. Being a dark stormy night, the waves of Yamuna water was in a fit of fury however parted to allow the carrier of the divine Krishna to pass. A gigantic snake recognized as Adisesha with 2000 hoods, glided behind them, its hoods made a shielding shelter over the child.
When Vasudev came back with Nanda’s child, the fetters fastened, the doors were closed and the guards awakened. Kansa came and lifted up the child to throw it to the wall and kill him however someway the baby slipped from his clutch and took the shape of a Goddess laughing at Kansa, she was nowhere to be found after revealing him that the one who would kill him had already been born and was elsewhere.
Krishna was the heartbeat of Gokul, as a small boy, a naughty prankster who was much loved amongst the Gopikas. He would steal curd and butter from the houses of gopikas. Though he was a child, yet he did numerous miraculous works. His exploits are now the everlasting legends of Braj. He killed a number of ‘asuras’(devils), vanquished the Kali Nag and later he killed Kansa as it had been predicted.