When a dog becomes part of a new pack of peers (whether dogs or people or both), there is an instinctive effort by which the dog puts himself into the social hierarchy, and this is not a one-time process, it's always subject to adjustment. The way a dog pack works, the way it survives to breed, depends on the pack's organization, which depends on there being a leader when one is needed. The process is simple and instinctive: the dogs are always challenging each other in ways which test their strength and resolve (that is, ability to serve well as leader in a crunch) against one another, and whoever wins moves up in the hierarchy. Tests are rarely harmful; most are primarily posturing things (play, races, mild fighting, etc.).
It's easy to make the mistake of attributing intent. The dogs strive against one another and whoever wins claims a prize: clearly they all want to win, right? But studies have shown the dogs that win are often less happy, and less healthy, than those who lose. And dog behavior makes clear that dogs don't resent losing; they seem to like it. The instinct doesn't tell them "I want to be a leader"; it tells them, "someone's got to be leader, so if no one else can do it, I will." There's some sense in which an animal might have more predisposition to become a leader -- probably not much of that is inborn, but a lot of it is learned during puppyhood when this struggle plays out within the litter. But no dog is so set on being an alpha, or not being an alpha, that they can't (when circumstances change) take on a different role.
When we anthropomorphize these behaviors, we imagine dogs are thinking like what some human might, and we all know humans who want to be in charge, or hate to be in charge, or feel pressured in some role life has led them to which doesn't suit them. But maybe we're getting it backwards. Dog behavior and human behavior are different, but when they're similar, maybe dogs tell us more about humans than humans tell us about dogs.
After all, we imagine that we are ruled by our thoughts, but there's tons of evidence that a startlingly large amount of the time, our thoughts are rationalizing what our instincts would have us do. And that makes sense: we were instinct-driven far, far longer than we've had higher brain functions, so for higher brain functions to evolve, to come into a home where instinct had ruled for millions of years, the higher brain functions had to be the ones to adjust. How many of our thought patterns are shaped by the need not to contradict our instincts, to justify them and get along with them? I don't just mean our tendency to embrace the illogical; it goes far deeper, with even our most humdrum and unthreatening ideas probably being servants of our instincts far, far more often than they are rulers of our instincts.
So how often are people being bossy because some instinct tells them that there needs to be a boss, and their thoughts rationalizing them into thinking they like it better that way? How many of the thousands of things that you "just like" without having a reason why you like this and don't like that are explicable only in terms of your instincts driving you to them? How many of the ones that you think you have a reason for, are really your instincts dragging you somewhere and your mind quickly deciding "oh, I want to go that way" only after you're already going that way?
The breadth of what mankind's brains have accomplished is only made the more extraordinary if you consider the very real likelihood that it spends most of its time compelled to find reasons for doing what's going to happen anyway, so it won't break under the strain of fighting against the rest of itself.