Many may assume that the chanting of the Hare Krishna ‘Maha-Mantra‘ is a modern phenomenon. Actually it is an ancient practice that was widely propagated in medieval Bengal by the most recent and most special incarnation of Krishna, who came in the form of his own devotee, Sri Krishna-Caitanya.
“As stated in the Srimad-Bhagavatam, the incarnation in the Age of Kali is Lord Caitanya Mahaprabhu, who spread the worship of Krsna by the sankirtana movement (congregational chanting of the holy names) and spread Krsna consciousness throughout India. He predicted that this culture of sankirtana would be broadcast all over the world, from town to town and village to village. Lord Caitanya as the incarnation of Krsna, the Personality of Godhead, is described secretly but not directly in the confidential parts of the revealed scriptures, such as the Upanisads, Mahabharata, Bhagavatam, etc. The devotees of Lord Krsna are much attracted by the sankirtana movement of Lord Caitanya. This avatara of the Lord does not kill the miscreants, but delivers them by His causeless mercy.”
Bhagavad-gita 4:8 Purport