Because most aggressive behavior involves fear or anxiety of some kind, training designed to resolve the discomfort underlying aggression work far better than domination and power plays. Techniques like desensitization and counter-conditioning are particularly effective. ¹
In some pet dog packs, there is a clear rank order, with one “top dog” and the rest falling in line like rungs on a ladder. In other packs, the order of the dogs depends on the resource. For instance, one dog is the boss when it comes to food, and another is the boss when it comes to toys. In still other packs, there appears to be no ranking of the individuals at all. They follow more of a “finders keepers” rule for determining who gets what. Finally, some dog 
packs just seem to share things without strife.¹
Dominance among dogs seems to be a function of age, size, reproductive ability, status history and motivation. Older dogs are often more likely to dominate younger dogs. Sexually intact dogs are more likely to be dominant over altered dogs, especially if they’re males.
The status quo can have a major impact on who’s dominant. A dog who has held the top position for some time may keep it, even as he ages and his physical abilities deteriorate. Prestige sometimes carries more weight than power. Once a relationship between two individuals is established, the subordinate animal defers to the dominant animal, and the dominant animal may, in turn, rule over the subordinate. In dogs, these relationships are reinforced through a sophisticated language of highly ritualized postures and gestures. Although dominance relationships are normally stable, certain events, such as the death or departure of a group member, the addition of a new member or the sexual maturation of a young animal, can trigger upheaval and restructuring of the hierarchy.
When animals and people are afraid of something, they prefer to get away from that thing. This is called the flight response. But if escaping isn’t an option, most animals will switch to a fight response.
They try to defend themselves from the scary thing. So a dog can be afraid of a person or another animal but still attack if she thinks this is her only recourse. A fearful dog will normally adopt fearful postures and retreat, but she may become aggressive if cornered or trapped. Male and female dogs are equally prone to fear aggression, and this type of aggression is common in both puppies and adults.¹
In my experience with dealing with fosters, the Bostons that were more likely to exhibit this fear aggression behavior turned out to be young male Bostons in the 24 to 48 months age group. While intact dogs may have a higher tendency towards fearful aggression, spaying or neutering alone will not solve the problem once it has started. Effective treatment involves behavior modification, combined with anti-anxiety medication, if needed.
Here is another point of view for you to consider:
When dogs fight, it’s because something is causing them to feel stress. Violence among dogs is not normal – it’s a sign something is wrong.
Family dogs are usually not related to other dogs in the home or to the humans in the household, nor were they born into your social group but instead arrived as youngsters or even adults. The relationship between your dog, other dogs in the home, and the humans in the family was imposed on him. He was not born into it. It is therefore not his “pack.”
We also use the term “pack leader” to describe a dog’s human owner or caretaker. And we’ve been led to believe we must exercise our “leadership” by dominating our pets. But here’s the thing – your dog 
knows you’re not a dog. And he expects to have a different relationship with you than he does with other dogs.
Once again I went to our friends on social media for their input on this subject of fear aggression in foster dogs how to identify it, how to work with it.
Anya Woronzoff: The best results we got with Rudy was seeing a licensed behaviorist, but we had to shop around for one we liked. There were some who used a lot of choke leash correction stuff that did not make us happy because it seemed cruel. Rudy was new to us and did not trust us, and we wanted him to trust us not fear us. Instead we went to someone who was all about positive enforcement. We found Rudy's "high value" reward treat and used that first to get him to trust us and then to start working with other people. We also taught him how to use a "safety mat"... it was just a mat we got that became his safe place (kind of like a crate) we trained him to go there and stay there when the doorbell rang and we asked people not to look, talk or touch him. It began to feel like his safe zone so we started doing the same thing at parks and the vet. He still uses it today, but now he knows to come off the mat when he is ready to greet someone. I was pretty skeptical at first, but that mat trick is amazing. We also did tons of other stuff: trips to the vet without getting any checkups, trips to Petco without stepping inside. Everything became a lesson in building his confidence. We've had him for about three years now. He's not perfect by any means, but he can greet new people, go to the vet without incident, and go to day care, so we are pretty pleased with the results.
Lori Kozielski: We tried a behaviorist with our Frazier and it helped quite a bit. He has been on prozac 
for nearly 10 years now. One of the other things the behaviorist recommended was desensitization by taking him to the park and exposing him to other dogs passing nearby, in a nonthreatening way. This, as well as private trainers, helped somewhat, but we came to the conclusion that this was as far as Frazier was able to progress. At this point he is able to be around my kids, my mom and a couple of friends. When anyone else comes to the house he is safely crated away. I do feel like he's missing out on some of the fun in life, but the alternative would be unthinkable. Hope that helps.... Unfortunately, our Boston is deaf so we can't do that. I use a gentle touch and signs to show him he's good. Other people can't get close enough, because he turns into the Tasmanian devil with his snarling...
April Argo: I had a fearful little Chihuahua one time, and I crated her right next to the door while people came in and out of the house. I told everyone who came in to just talk to her but don't stick their hands or anything in the crate. After several months she did finally come around. Wire crate where he can see them come in and out, just ask them not to touch him, and ask them to pretty much ignore him, but allow them to walk by real close (not close enough to get bit, of course), or stand there a minute ignoring his gestures or aggressive behavior. Our chihuahua would back up in the corner of the crate and sometimes even growling, but if the person didn't show fear or didn't try to touch her, she would sit there a bit and calm down.
from an unknown source on breaking the cycle of aggression in dogs:
Avoid potentially dangerous situations. Do not do the things that cause an aggressive response in the dog, whether it is staring at the dog, hugging it, or disturbing it while it is sleeping. If the dog growls when her food dish is handled, give the dog something else to do while the dish is removed; fetching a ball, going for a walk. Do not use any treats or toys which may cause the dog to become possessive. If the dog starts to show any aggression, re-direct her attention. Take out the leash, or a favorite toy, and ask the dog to come to you and sit. You can also just walk away. Later, when the dog is calm and comes to you for attention, ask her to sit or lie down before you pet her. Keeping a long leash on the dog whenever she is inside can help you to move the dog when needed.
Mya Chuskie: And respect the dog. I can't stand people who think they can touch the dog without 
permission. I always followed the no-touch-talk and eye contact ever since I remembered handling dogs. Let the dog check you out first then if he wants affection they will stay around. Give them space just like we like our space to.
If you notice signs or symptoms of inter-dog aggression you should contact a local dog trainer or your veterinarian to seek advice to help your dog.
² Applied Animal Behaviorist Dr. Karen Overall of the University of Pennsylvania