The picture is so sick, it's disturbing. Notice the body language of the recruits -- kneeling slaves about to be shackled. And priest, stern and convinced no one will notice how strange his behavior is.

Most societal animals have a military, how is that a human invention?!?

Killing machines on both sides. One kills your body, the other kills your mind.

A tremendous waste of resources all around.

Good post. We have to look deep into human evolution to see the causality and connection of the two. Picture hundreds of thousands of years as primitive hominids, something like are present-day Amazon Rain Forest tribes, called hunter/gatherers. So when agriculture came along everything changed. It is here that both religion and the military proliferated.
One farmer could feed the whole village so a protection class emerged. Tribes became mega-tribes and eventually a country developed, first was probably Sumeria in the Fertile Crescent. This is when large city/states developed. A group could accost the farmer promising to protect his land and keep it in the family, bringing about a scribe/priest class. Next to the farmer these were the first two specializations of labor.
Here's where the beautiful scam came about. The land owner could promise the peasant if you work hard you have a soul and the gods will reward you.

I sometimes reflect on the incredible waste associated with maintaining all the military forces around the globe and think about how much better the planet and all life would be if we used those resources for the common good.