It obviously wasn't a fast transition, but Christianity brought around the concept of absolute religious equality. A novel idea to the world, and likely the cat

It obviously wasn't a fast transition, but Christianity brought around the concept of absolute religious equality. A novel idea to the world, and likely the catalyst that changed thousands of years of slavery. I know it isn't in fashion to credit Christianity with anything, but what other philosophy of the era could have eventually ended slavery, given slavery is likely the state of man ever since Grog the caveman threatened his brother-son with a beating if he didn't fetch more water.