Ascend Hand of Kul

A very easy place to get this is during the tutorial. When you learn how to round up your worshipers bring them with you and once the tutorial comes up telling you how to stomp the enemy humans (Don't stomp them) they will as far as I've seen infinitely spawn. Just drop your worshipers and let them rack up kills until the achievement pops.

The best place to do this is during the tutorial but it can be done anywhere where you have ally humans and a rival village with plenty of enemy villagers.

In the area called Crimdol wall there is a village called Gatehold and just before that there is a small army of villages you can pick up press UP on the D-Pad. This basically turns you into a small mobile archer tower. Meaning you can move about and let your human allies pick of enemy humans/other enemies at will and the best thing is there kills of ANY enemy counts towards the achievement. Even enemy humans who die in 2 hits!

To be honest this can be done in any village where you have allies to fight enemy humans but this village is the easiest as its the first you encounter.

Video below showing me having to return to it to reclaim it and then using my human allies to get me the achievement.

When you have the ability to round up your human worshippers you can send them in to battle for you. The best way to rack up kills is to guard against the larger enemies and let your minions whittle down their health. I believe you just need to make sure your humans perform the killing blow. You can attack the enemies to weaken them down to just a few bits of health and let them finish and it should count.

There are also times where your humans can fight other humans. This is probably the fastest way, but these situations don't come up too often. The enemy humans are easy to kill for your humans so just try and keep them off you and let your humans lay waste.