I don’t understand the psychology of aggression. What makes some creatures more aggressive than others?

For instance, let’s take dogs. Our current dog, Jake, is a stumpy tail cattle dog (that’s an actual breed) that we rescued from a shelter. He is cute and affectionate, and although he can get a little irritating (as all herder breeds do), he is a wonderful dog, except for one thing. He is highly aggressive towards other dogs.

Taking him on a neighborhood walk always carries the risk that there will be an altercation. When he sees other dogs approach, he will take a stance in the middle of the road and attempt to intimidate and dominate. I have learned that this particular breed is known to be aggressive towards other dogs, so this is probably genetics, and since we didn’t have him as a puppy, there doesn’t seem to be much we can do.

But my story of our dog is not the main point of this blog post. Here’s my main question: What makes some people naturally aggressive? Why do some seem to be born that way? Is it nature or nurture? What makes them want to dominate, to bully, encroach, take over, invade? Why does every schoolyard have bullies? What factors create the Joseph Konys or the Joseph Stalins of the world? What wars would never have started if there wasn’t an aggressor?

What are your thoughts on aggression?