An avatar in Hinduism is the highest authority ordained by Brahman, God on mother earth.
When society reaches a point of no return, faces its lowest ebb, to re-establish Dharma (righteousness) manifests a human being, a man god (enlightened one) coupled with powers of Chanakya (the most able administrator in the entire history of mankind).
To save lives of millions of countrymen and soldiers Chanakya got 100 kings eliminated in one day. The might of even Chanakya is unprecedented. But the power exercised by Chanakya is limited to manifest physical life, never the spiritual domain.
An avatar is an instrument of the spiritual world. To annihilate dark forces of nature manifests an avatar… a savior, messiah to set things right on mother earth. One amongst us, a commoner manifests so much power that people called him an avatar (God manifest in human form).
As detailed in Hinduism sacred texts life comes full circle every 3500 to 5000 years. Above 3650 years before in Dwapar Yuga in times of extreme life, tribulation advent Lord Krishna, an avatar of his era. In the present troubled Kali Yuga people await advent of Kalki Avatar, the annihilator of dark forces of nature, Kali Yuga.
Between 2022 and 2025 mankind would witness advent of this one-man army, Kalki Avatar. Such would be the might of this enlightened soul that he shall shortly develop a dedicated following of 2000 million people worldwide. Another 1000 million people would further follow him.
The advent of an avatar is always to re-establish Dharma (righteousness) against evil forces of adharma (lawlessness). The advent of an avatar occurs when a battle of Mahabharata magnitude is about to precipitate. The awaited world war 3, a war of Mahabharata magnitude, a full-scale nuclear war would result in death of almost 20% population of world, about 1200 million people.
After such a man-made calamity the only solution lay with an avatar. Mounted with power of Bhagavad Gita and Upanishads (independent a spiritual treatises) such an enlightened one finally succeeds in bringing Satyuga (the awaited golden period). The teachings of Bhagavad Gita from an avatar acts like a soothing balm to the ailing world community.
People remaining the same worldwide, only the perception changes! Earlier people were practicing negativity 95% and only 5% were truthful. In a Satyuga 95% people practiced truthfulness and only 5% negativity.
The concept of an avatar exists in spirituality never religion (path of rituals).