History of Lord Krishna:
Lord Krishna appeared over five thousand years ago in Mathura, India to Devaki and Vasudeva in the jail cell of the tyrant Kamsa. The place of His birth is known as Sri Krishna Janmasthana. He appeared with His brother Balarama in response to the demigods' prayers for protection from the widespread influence of demonic administration on earth.
Previously, the demigods and demons had been at war in the heavens. When the demons were defeated by the demigods, they decided to instead attack this planet earth. Thus, they invaded the earth by discretely taking birth as princes in powerful royal families of the time.