CC Antya 3.50
go-brāhmaṇe hiṁsā kare mahā durācāra
From this statement by Śrī Caitanya Mahāprabhu we can clearly understand that the word yavana does not refer only to a particular class of men. Anyone who is against the behavior of the Vedic principles is called a yavana. Such a yavana may be in India or outside of India. As described here, the symptom of yavanas is that they are violent killers of cows and brahminical culture. We offer our prayers to the Lord by saying, namo brahmaṇya-devāya go-brāhmaṇa-hitāya ca. The Lord is the maintainer of brahminical culture. His first concern is to see to the benefit of cows and brāhmaṇas. As soon as human civilization turns against brahminical culture and allows unrestricted killing of cows, we should understand that men are no longer under the control of the Vedic culture but are all yavanas and mlecchas. It is said that the Kṛṣṇa consciousness movement will be prominent within the next ten thousand years, but after that people will all become mlecchas and yavanas. Thus at the end of the yuga, Kṛṣṇa will appear as the Kalki avatāra and kill them without consideration.