Kansa: The story before Krishna's birth .
If we see the relation of Mama(maternal uncle )then there is a very respectful relationship. The sound of the word Mama is pronounced twice in the sound of the word Maa(mother). But in the mythological history of Hindus, there have been two maternal uncles who have made this relationship the object of ridicule and cruelty forever. A maternal uncle Shakuni, a maternal uncle Kansa and both happened at the time of Lord Sri Vishnu's Krishnaavatar. While Shakuni was the maternal uncle of the Kauravas, Kansa himself belonged to Lord Krishna.
Kansa is one of the biggest villains of our Indian mythology. His sins were so strong, ruthlessness so intense and tyranny was so inhuman that Dwapar yuga was shivering in his name. He found the name of Kansa Mama in history by ruthlessly killing six children of his own sister Devaki. Even today, when a maternal uncle crosses the limits of his relationships, he use to received the title of Kansa Mama.
It is also known to famous in world that Kansa really loved his sister Devaki very much. His love for Devaki was so intense that Kansa himself carried his sister's doli (palanquin) on his shoulders at the time of her departure after marriage. Kansa was frightened after the listening of Akashvani, which announced that, he will be killed by Devaki's eighth child. And he committed atrocities, which cannot be compared to anyone in history nor imagination.
Despite being children of religious parents, how did such devilish tendencies awaken in him. He loved his sister more than life ,but how he could torture her? The answer to all these questions is one and it is astonishing - Kansa was not the real brother of Devaki! how,
Kansa was an Asura in his previous life!
There is no doubt that Kansa was powerful and had immense knowledge of weaponry. On his strength, he ruled in Mathura for years. But this is a matter of thinking that how can a human being be so cruel that his own sister, brother-in-law, parents can be imprisoned. Try to kill the unborn nephew. He wreaked havoc on the public and did all the work that indicated demonic tendencies.