Lord Vishnu always incarnates at the end of a Yuga when the society almost reaches a point of no return. The end of a Yuga means precipitation of a man-made calamity, a mother of all wars. In present times humanity awaits rather fears the coming world war 3. The deathblow of this silent killer (world war 3) would be totally unbearable.
The advent of an avatar announces coming of a new era!
To annihilate dark forces of nature, the present Kali Yuga advent of an avatar is an absolute must. Unless Lord Krishna incarnates, Dharma (righteousness) cannot be re-established. To put the society back on its pedestal, coming of an avatar of present era, the awaited Kalki avatar is an absolute must, something ordained by God himself.
Kalki avatar would not be different from us except for his indomitable willpower and willingness to survive the odds even when faced with evil of the highest order. In times of need one amongst us dawns the mantle of an avatar. That ordinary mortal has to be a self realized soul, nothing less. It is power of Bhagavad Gita and Upanishads (independent spiritual treatises) that converts this humble human being into a superhuman.
An avatar never comes from the top as believed by many worldwide. Indulging in chintan, churning self inside out a commoner amongst us manifests so much power that humanity calls one an avatar (God manifest in human form).
To end present Kali Yuga and usher mankind into awaited Satyuga, the golden period there was no other alternative for Lord Krishna other than manifesting form of Kalki avatar.