The fact is that most excessively dominant people are usually bullies. Bullies are deep-down very insecure people. They dominate because they are too insecure to allow other people to have responsibility and influence, and this behaviour is generally conditioned from childhood for one reason or another. The dominant bullying behaviour is effectively reinforced by the response given by 'secure' and 'non-assertive' people to bullying. The bully gets his or her own way. The bullying dominant behaviour is rewarded, and so it persists.
Dominant, bullying people, usually from a very young age, become positively conditioned to bullying behaviour, because in their own terms it works. Their own terms are generally concerned with satisfying their ego and selfish drives to get their own way, to control, to achieve status (often implanted by insecure ambitious parents), to manipulate, make decisions, build empires, to collect material signs of achievement, monetary wealth, and particularly to establish protective mechanisms, such as 'yes-men' followers ('body-guards'), immunity from challenge and interference, scrutiny, judgement, etc. Early childhood experiences play an important part in creating bullies. Bullies are victims as well as aggressors. And although it's a tough challenge for anyone on the receiving end of their behaviour they actually deserve sympathy.