The Sun is round, our world goes round in circles, Stonehenge, boobs and even atoms, all round. We are surrounded by round things, our universe governed by circles.
As certain as night follows day, sadness and happiness, down and up, why shouldn't cycles and circles prevail.
There's the short business cycle (I'd put that around 7 years, much like a 7 year itch) or longer Kondratiev wave (40 - 60 years).
The good times will return, it's just that we can never pick the bottom nor estimate the timing.
Have we Christians had our turn? With the Crusades, we nudged out the Saracens. Has the circle turned, we've had our 500 years and now it's time for Islam to be the dominant religion.
The industrial revolution ushered in the great western power. Industry, capitalism, mass production and consumption.
The Eastern civilisations all but disappeared. The Spanish conquest crushed the Aztecs. We're now probably seeing the resurgence of the Chinese, Indian and South American empires.
So many questions, no bloody answers.