Kansa ascended the throne of Mathura after ousting his father, Ugrasena at the behest of his closest aides Banasura and Narakasura. He expanded his kingdom by engaging in diplomacy with Jarasandha, the King of Magadha. And with his assistance, Kansa grew stronger and more powerful.

Was Kans really powerful?

Enhanced Strength (Kans was physically stronger than most in his setting, though he did not like to engage in personal conflict without the use of his sword - prefering to have his soldiers or demons do his work for him : he was shown as strong enough to break stone with his fist.)

Who is powerful Ravana or Kansa?

RAVANA WILL BE BECAUSE HE HAVE VARADAN OF SHIVJI AND MANY MORE REASON ND HE HAS MORE POWERS THAN KANS AND HEBIA THE KING OF LANKA SO THATS WHY HE IS MORE POWERFUL THAN RAVANA.