The birth of Krishna is in itself a transcendental phenomenon that generates awe among the Hindus and overwhelms one and all with its supra mundane happenings.
Mother Earth, unable to bear the burden of sins committed by evil kings and rulers, appealed to Brahma, the Creator for help. Brahma prayed to the Supreme Lord Vishnu, who assured him that he would soon be born on earth to annihilate tyrannical forces.
One such evil force was Kamsa, the ruler of Mathura (in northern India) and his people were utterly terrified of him. On the day Kamsa's sister Devaki was married off to Vasudeva, an akashvani or voice from the sky was heard prophesying that Devaki's 8th son would be the destroyer of Kamsa. The frightened Kamsa immediately unsheathed his sword to kill his sister but Vasudeva intervened and implored Kamsa to spare his bride, and promised to hand over every new born child to him. Kamsa relented but imprisoned both Devaki and her husband Vasudeva.