Do rats fight over territory?

Question
Hello Debbie. My name is Julie and I have two male rats. I have not have any problems with them, but I do have a question on whether male rats fight over territory as a member of a Korean rat online cafe has stated that
* Rats do not fight (to an extent of drawing blood) over territories
* Therefore it is safe to just plop them in together without any pre-introduction
* This is safe because domesticated rats do not have a sense of strong territoriality, due to their highly social nature
* Territorial behaviour is only seen in solitary animals, not in social animals that feel lonely when alone
* Rats like all larger animals, because they are domesticated to like humans and they relate humans to all other larger animals (and this is seen in cases where rats make friends with dogs and cats)

I am a postgraduate biology student in animal behaviour, conservation and ecology, and I do NOT believe in any of the statements made above. I am an active member of the online cafe and have a blog on rat keeping, because information on rat keeping is scarce in Korea and I would like to do everything in my power to reduce incorrect rat handling and keeping to ensure the mental and physical health of as many rats as possible.

So this person (Ill call her/him DD) has said all statements above, and seems like all those beliefs come from his/her own experience of just plopping new rats and old rats together with no negative outcome.
There is one member on the online cafe who is having problems with her new rat and the old rat, and DD says that it is only a fight to decide on the hierarchy and not territorial at all.
These two rats are males, 6 and 4 months old, and are fighting hard enough to draw blood (the old rat is constantly attacking the new, even outside the cage and is persistent) and have even drawn blood from the hand of the cafe member.

How could I convince DD that domestic rats do show territorial behaviour and that they will fight to defend their territory? I have linked a few websites (including yours on rat introduction and a scientific research paper using the territorial behaviour of lab rats) but this person is super stubborn, going only off his/her own experience with no proof to back up his/her theory/opinion. (this person is also unhappy that i could only find these info in english, as there are hardly any reliable info on rat keeping in Korea)
I really would like to prevent people from getting the wrong info, resulting in numerous rats experiencing needless stress.
So DD is saying that he has never heard of a case of rats fighting over territory, so I am trying to get some stories on rats territorial fights.

I am so sorry for the super long email, any kind of reply would be much appreciated! Thank you so much for taking your time to read this email.
Kind regards
Julie

Answer
Hi Julie,
It sounds like she already has her mind made up, but you can try referring her to this link
http://www.ratbehavior.org/WildRats.htm

Apparently some lines of domestic rats have been bred to the point where they are very docile and show little territoriality, and perhaps she has had experience with some of these rats. But in domestic rats as a whole, most rats are aggressive toward newcomers, at least for a while, and especially if the stranger is in their home cage.  I don't know what other information would convince her.
Deb