Where do the monsters come from?

I recently watched a movie that started off with a bang when a peaceful human village is attacked by a horde of large, orc-like monsters. Between the grisly, flesh rending scenes, I noticed many details about the monsters: (Let’s ignore that they were played by human actors, which dictated much of their form and just go with the direct observations. )

• Though they had faces that “only a mother could love” there is evidence (torso structure and arm aticulation) that they were of hominin descent. This means that they use sexual reproduction, and some members of their society are probably dedicated to child-rearing. Monsters don’t just spring up like wildflowers.
• They wore leather clothes and jewelry. This suggests that some members of this monster society are tanners and jewelers. It also gives us an indication that they have some concerns about personal grooming. 
• They used distinct Iron Age weapons. They weren’t stolen, so they have some working knowledge of metallurgy. This is not insignificant.  Stupid beasts do not become blacksmiths.
  • How many of us were surprised that there are Klingons who are lawyers, scientists, and even bookkeepers? We shouldn’t have been.
• They communicated and worked as a team. 
• They are demonstrably carnivores who have a particular taste for human flesh. 
• While the individuals shown on the screen were a fighting unit, they were not particularly effective as warriors. Though they outweigh a typical human by two or three times and clearly use this to be intimidating, they are easily outmatched by humans with even a modicum of martial ability. One monster was defeated by a woman who went all “momma bear” with a kitchen knife on his ass.

Now for some speculation:

• Monsters probably don’t think of themselves as “Monsters” unless we include a Pixar series of cartoons. Bad Guys never think of themselves as the Bad Guys. Even Nazis didn’t think of themselves as the bad guys. So what is their motivation for attacking a peaceful human village? They could hunt other animals who don’t have sharp, pointy metal things to fight back with. Though the humans won the battle only with the intervention of magic, the monsters lost a good percentage of their group in standard melee battle against mostly untrained humans. Is it really worth the cost to hunt humans? Cows don’t fight back. 
• Given the above speculation, I’m going to further speculate that they attacked the humans because:
  1. They were ordered to.
  2. They have the bigotry of religious zealots against humans.
  3. They thought they were defending their territory against the humans. This one’s a little difficult to sell considering the monsters had to march a great distance to find the humans. 

I suspect that the individual monsters really had no idea why they attacked the humans. In the movie, it turns out that the Arch-Bad Guy was looking for humans who would eventually challenge his Evil Empire, and was practicing a parched earth policy approach to the problem. 

I can imagine the pre-march speech made by the Arch-Bad Guy: “The humans eat your babies! They are forcing your children into slavery! They want to take away your swords! They worship false gods! You must be prepared to die for our holy war against the humans!”

Hey! Monsters have agency, too!