The Hindus believe that we're living in the Kali Yuga, an apocalyptic Dark Age ruled by the demon Kali, the source of all evil and destruction. The Kali Yuga, also known as the "Age of Vice," is a period of warfare, chaos, social decline and spiritual decadence brought about by Man's separation from the gods. Kali himself is frequently pictured as a deranged figure dancing on corpses and wearing human heads as jewelry. I don't believe in demons, but this bloodthirsty lunatic with ten arms is the perfect symbol of human history.
Some writers use the term Kali Yuga to mean "end times" or the "last days," but that isn't accurate. The Hindus see Time as a cycle of four ages or Yugas known as the Yuga Cycle. The other three periods are called the Satya Yuga, the Treta Yuga and the Dvapara Yuga, and they all go spinning around like a cosmic ferris wheel. So the Kali Yuga isn't the end of the world. It's just the end of one cycle and the beginning of the next.
The Yuga Cycle describes a fall from grace--a loss of enlightenment. The first age, the Satya Yuga, is a golden age of supreme goodness when the gods rule and the average human lifespan is 100,000 years, but, like the Garden of Eden, it's all downhill from there. The other Yugas follow in order, the gods withdraw, the situation deteriorates and bottoms out with the Kali Yuga, then the whole thing starts all over again. Time is a circle--an infinite, recurring progression of Yugas in which the gods advance and retreat like the tides or the phases of the moon.
Now, this is good stuff and very ancient, but is it an accurate description of Reality? That probably sounds like a strange question to ask. The Yuga Cycle is a symbolic, mythical cosmology, a metaphor, I think, for the Hindu concepts of karma and reincarnation. Taking it literally misses the point, but is it possible that Time is actually circular? Does the Yuga Cycle or at least its concept of Time have some basis in fact? Personally, I think the idea of circular Time is more interesting than the linear Christian view of history as moving in a straight line from Creation to Apocalypse, but I don't see any evidence that the universe actually runs in cycles like this.
Time is a one-way thing. The future changes into the present which changes into the past in an infinite stream of Becoming. There are cycles in nature, but they're more like recurring patterns with thousands of variations and they never repeat themselves in exactly the same way. The fossil evidence shows a gradual evolution from the simple to the complex punctuated by catastrophes, mass extinctions and sudden bursts of new life forms like the Cambrian Explosion. If there are cycles in nature, they are cycles of chaos in the mathematical sense. The gods of this world are fractals and strange attractors.
Human history repeats itself, but only in the sense that high cultures are subject to universal laws of growth and decay as described by Oswald Spengler. Personally, I think there's a good argument that civilization in general has deteriorated over the last two thousand years, but I'm more inclined to blame it on the Second Law of Thermodynamics than the Yuga Cycle. Entropy and chaos are the natural state of things and organized systems tend to deteriorate over time. It takes energy and intelligence to keep a civilization going and both are in short supply.
The Yuga Cycle is appealing because it explains the decay and turmoil we see around us and because it suggests that things will change for the better as the cycle turns once again. Unfortunately, these cycles are so long that they don't really have any meaning for the human race in general, never mind individuals. The Kali Yuga is supposed to have started around 3000 BC and they say it will last for 432,000 years, almost half a million years. Considering the fact that only 5000 years or so have passed since the Kali Yuga started, we've got a long way to go.