Why do human beings create divides in order to separate people from one another?

The reason you don't see this in the animal kingdom is because humans aren't animals. We have so many things going on that animals don't have. We can reason. We have a sense of morality. We feel anger, jealousy, fear, etc. But we also feel love, compassion, empathy, etc. As an example, if a lion in Africa takes a carcass away from a hyena, it wasn't out of meanness or envy, or because he thought he was better than the hyena. He just saw a meal and needed it to live. Likewise, the hyena doesn't get mad and hold a grudge, or vow vengeance on all lions or demand justice. He just goes and looks for more food. And the other animals watching don't step in to "right this wrong" and take a collection to feed this poor animal that has had his meal stripped away. No, they just go about whatever they were doing. Contrast that with how humans would view a similar situation and lines would be drawn in the sand. Right now as I type our leaders are telling other leaders that if they use chemical weapons on civilians that we'll take action. And IMO that's a good call. But if we were just animals we wouldn't care about some people on the other side of the world.

I disagree with your statement "Religion, race, politics, national boundaries, classism; none of these are real." They are most certainly real. Saying they don't appear in nature is incorrect unless you mean they don't appear in the animal kingdom. But I already addressed that humans and animals are not on the same level. The Bible makes this distinction very clear. It says that God made man in His own image which means we have His attributes. Justice, right, wrong, love, compassion, etc. are things we have that animals don't. The reason all of this turns us against each other is because of sin. While we're still made in the Creator's image, we're now bent toward evil and that is very apparent in the world and has been since the fall.

We are still human are regardless of all those things we still have the free will to choose how we treat each other... all that other stuff is either an excuse to act or an excuse to hate. But not of that is the cause.

Um, Im pretty sure the above is not true. Bands of Chimpanzees often fight each other over territory. Groups of tigers fight each other. Packs of dogs. Pretty much an group of animal will fight for territory. Its pretty normal behavior. Banding together into small groups based on family, genetics etc - pretty darn normal across the board. Fighting others outside your group also normal.