A small correction to splitrocket's write-up above... The advent of the Kalki avatara is predicted in the Vedic literatures, thus:
athasau yuga-sandhyayam
dasyu-prayeshu rajasu
janita vishnu-yashaso
namna kalkir jagat-patih

Therafter, at the conjunction of two yugas, the Lord of the creation will take His birth as the Kalki incarnation and become the son of Vishnu Yasha. At this time the rulers of the earth will have degenerated into plunderers.

(Bhag., 1:3:25)

True, this will signal the beginning of the end, however the dating of this is slightly out. The present Kali-yuga lasts for 432,000 years, and only five thousand years have passed since the Battle of Kurukshetra, the end of the régime of King Parikshit, and the passing of Sri Krishna. Thus, it will be in approximately 429,000 CE that this will occur.