Theomachy

The Frail Circle of Life

Theomachy, more commonly known as the War of Gods, is almost an universal concept of cosmological powers fighting each other. It is not restricted to only one pantheon of gods, but is as much a religious as also a philosophical notion.
It is thought to be a cycle of life, in both cosmological and mortal way; as without higher powers, the universe will collapse when magic deteriorates. The cycle hasn't stopped since the time immemorial; it always repeats itself in the stages of birth, life and death. No one knows what happens if that cycle stops.

Summary

The details on how and why the War of Gods is fought depends completely on the entity.
The general consensus is that the fight has been going on for millennia, ever since the world was created and gods were either born or had recently arrived to the new fresh world. Either way, this meant they were in an infantile state. Slowly, during the years, different entities gathered followers, until it was inevitable that some higher powers would start to clash, therefore giving birth to the concept of the War of the Gods. During centuries the warfare would slowly start to escalate, and when it did so, normal people would start noticing. First to go would be those small entities, mostly local guardians and elder spirits which had only thrived due to their local followers, who often turned to other gods when the powers of the entity they originally followed started to fade, thus just weakening it further. And when a higher power would not have a single follower left, it would start to die away, and its domain and powers would be up to first one to snatch. Many gods, especially evil, grew in power that way, when they would slowly kill or convert all believers of a lesser power and then, when that entity would be no more, they would snatch what was left, sometimes ending up with a very mismatched portfolio.
The Grand finale of the War of the Gods would be the Great Battle, where forces of good and bad would counter each other on battlefield. Many entities would die that day, and it is often depicted as a very perilous fight for the higher powers, and usually it would be such an even fight that even single, otherwise unimportant entity, would end up tipping the scales for the favor of which side it would be serving on. Therefore it could never be known what would happen after the great battle. Would the circle continue, or would it finally reach its end? So far the cycle has continued; from the ashes of old powerful ones sprout new ones, and the cycle repeats itself yet again.
As hinted before, the whole concept of Theomachy is of cyclical nature, which reflects the natural progression of life: We are born, we live and grow stronger, until we battle the old age and die. So far as it is known, the cycle has continued unbroken from the beginning of the time, but after the Great Turbulence shook the whole world of Altaros almost 700 years ago, rumors have been going around that the circle might, unlike it should, have an end.

Historical Basis

Among the scholars there is a consensus about the cyclical nature of history. In history, great battles are often fought during a certain period of time and the common unrest and unhappiness rises during those periods. Sightings of eldritch horrors, undead and records of mortals turning more vicious, ruthless, and even evil, will start to appear more frequently as well.

Spread

This myth has spanned all over the world in different forms, but often changed shape in a way that it can be hard for unlearned to spot. Still, this is common knowledge in more uniform state for many clerics who have had even a little bit of religious studying.