SB 10.2.1

This verse supports the following statement given by the Lord in Bhagavad-gītā (4.7-8): yadā yadā hi dharmasya glānir bhavati bhārata abhyutthānam adharmasya tadātmānaṁ sṛjāmy aham paritrāṇāya sādhūnāṁ vināśāya ca duṣkṛtām dharma-saṁsthāpanārthāya sambhavāmi yuge yuge “Whenever and wherever there is a decline in religious practice, O descendant of Bharata, and a predominant rise of irreligion — at that time I descend Myself. To deliver the pious and to annihilate the miscreants, as well as to reestablish the principles of religion, I Myself appear millennium after millennium.” The Lord’s purpose in maintaining this material world is to give everyone a chance to go back home, back to Godhead, but kings and political leaders unfortunately try to hinder the purpose of the Lord, and therefore the Lord appears, either personally or with His plenary portions, to set things right. It is therefore said: garbhaṁ saṣcārya rohiṇyāṁ devakyā yogamāyayā tasyāḥ kukṣiṁ gataḥ kṛṣṇo dvitīyo vibudhaiḥ stutaḥ “Kṛṣṇa appeared in the womb of Devakī after transferring Baladeva to the womb of Rohiṇī by the power of Yoga-māyā.” Yadubhiḥ sa vyarudhyata. The kings of the Yadu dynasty were all devotees, but there were many powerful demons, such as Śālva, who began to persecute them. At that time, Jarāsandha, who was Kaṁsa’s father-in-law, was extremely powerful, and therefore Kaṁsa took advantage of his protection and the help of the demons in persecuting the kings of the Yadu dynasty. The demons naturally appeared more powerful than the demigods, but ultimately, because of help received from the Supreme Personality of Godhead, the demons were defeated and the demigods triumphant.