More than a century ago, the old world ended in fire, death, and destruction.
After unheeded warnings and portents, the old Gods and the powers they granted to their priests disappeared. Next the arcane magics of the wizards became unpredictable and dangerous, sending magical storms and summoned horrors rampaging across the land.
Then the world itself went mad. Fire rained from the sky, savage monsters ravaged, disease and starvation were everywhere. Rivers and seas left their banks, the season changed every week then changed again, and night and day became irregular and unpredictable. Crops and livestock failed and died, cities disappeared, Kingdoms fell. Tens and hundreds of thousands suffered and died, and all aspects of civilized order disintegrated.
Some exceptional men and women refused to accept chaos death. They kept their families, clans, or small bands of followers alive in a world seeking their destruction. They migrated, they defeated monsters, and through courage and stubborn force of will, they survived.
Eventually these exceptional leaders died, usually after unnaturally long and amazing lives. The stories told about them were passed down from one generation to the next, and continued to inspire their descendants and followers. Soon, a few of the followers of these departed heroes started to receive dreams and visions from the dead leaders. Dreams then became miracles, then divine spells and powers, usually granted to the direct descendants of the revered leader.
They became the New Gods, or the Small Gods. These infant Gods only have a few priests able to channel divine power, never more than five at a time, and usually only one or two. Most Small Gods have a few hundred followers, all living in the same small area.
Each valley, each hill, each stubborn little village full of stubborn survivors, has its own patron deity. In life, the people who became the Small Gods were clannish, tough survivors. As deities, they encourage the same qualities in their followers and human institutions remain small and fiercely tribal.
But now, rumors are spreading that the Old Gods have returned. Some say the old Gods are now angry at being forgotten and replaced. Others, whisper the Old Gods have gone mad, that perhaps their madness caused the world's destruction in the first place.
No one knows what their return will bring. But all sane people fear anything that might send their world back into the chaos and destruction it only just clawed its way out of.