When three fourths of the population of the whole world become irreligious, the situation is converted into hell for the animals.

SB 1.16.20 P   How Pariksit Received the Age of Kali

  With the progress of the age of Kali, four things particularly, namely the duration of life, mercy, the power of recollection, and moral or religious principles will gradually diminish. Since Dharma, or the principles of religion, would be lost in the proportion of three out of four, the symbolic bull was standing on one leg only. When three fourths of the population of the whole world become irreligious, the situation is converted into hell for the animals. In the age of Kali, godless civilizations will create so many so-called religious societies in which the Personality of Godhead will be directly or indirectly defied. And thus faithless societies of men will make the world uninhabitable for the saner section of people. There are gradations of human beings in terms of proportionate faith in the Supreme Personality of Godhead. The first-class faithful men are the Vaisnavas and the brahmanas, then the ksatriyas, then the vaisyas, then the sudras, then the mlecchas, the yavanas and at last the candalas. The degradation of the human instinct begins from the mlecchas, and the candala state of life is the last word in human degradation. All the above terms mentioned in the Vedic literatures are never meant for any particular community or birth. They are different qualifications of human beings in general. There is no question of birthright or community. One can acquire the respective qualifications by one's own efforts, and thus the son of a Vaisnava can become a mleccha, or the son of a candala can become more than a brahmana, all in terms of their association and intimate relation with the Supreme Lord.