Once there was a time Shri Narada Muni, the divine sage, visited Kansa. He spoke to Kansa about most of the inhabitants of Gokula, with Nanda as their head, were all Devas born on the earth at the command of Lord Vishnu to destroy all the Asuras living on earth. Kansa was taken aback.
Once again fear started seizing him. As soon as Narada Muni left the place, he chained Vasudeva and Devaki and imprisoned them in a dark cell. Kansa thought that it was his mistake to spare the life of their first child of Devaki & Vasudeva. He went to Devaki’s cell, snatched the child from her hand and killed him mercilessly.
He began to hate the Yadavas and started harassing them. He imprisoned his father Ugrasena also, since he was the leader of the Yadavas. He began persecuting the Yadavas, who had therefore to run here and there to save their lives.