Requires some set up, but generally easy to achieve.
Single player game
Huge map, Pangaea
Online speed
Ancient start
Reasonable difficulty - settler will slow the AI and you want them to get religions decently fast, but I wouldn't go above standard
No barbarians
Pick India.
And then pick India.
And then pick India a whole bunch more.
The trick to this achievement is to set every single AI civ to India. This way everyone prioritizes religions and you're fairly guaranteed to never be at war. Just don't antagonize anyone.
The general strategy is to rush for your own religion in the opening (fast holy site, +faith civics), and then build a whole bunch of scouts to find all the other civs. With no barbs, you won't need an army, and playing on a pangaea means you don't have to wait for ocean crossing to find everyone. With all the India AIs, the rest of the religions will be scooped up fairly quick. Assuming you've avoided war (which is easy), the achievement will pop.