Cat fighting over territory

One of my two cats seems to have adopted my bedroom as his territory. Zorro sometimes sits in the doorway waiting for my other cat, Spooky, so he can chase him away. This problem seems to be getting worse. Previously both my cats slept in my room but now poor Spooky is getting let out. During the night I am often awakened by the two of them wrestling. I yell at them and break it up. Then later, only Zorro is asleep in the room and poor Spooky is somewhere else. Sometimes when I wake, both cats are asleep, close on my bed (and look sooo cute!) and a few other times they will be sleeping close together in one of the cat beds. But most of the time Zorro tries to keep Spooky out. Somedays he extends his territory so that Spooky can't come upstairs at all. It's sad to find Spooky sleeping alone in the hall while Zorro is stretched out on my bed. (Which is often how I find them when I come home from work.) What can I do to get Zorro to share? Spooky was here first and always slept with me. They are about very close in age. Spooky is just a year old and Zorro is about nine months old. I tried letting Zorro know this is really my territory and putting him out of the room and letting Spooky in. But that didn't seem to work.
Anyone else have a problem like this with territory fighting? Any suggestions? Please help! Thanks.

Are they both neutered? It sounds like Zorro may be fighting for alpha male position. Once that is established, he may calm down and let Spooky come back in the bedroom.

Yes, they are both neutered. Usually cats don't fight for territory if they are neutered, right?

Retrieved this from another website - hope it helps..

Dominance/Hierarchy in Cats
===========================
Cats in multiple cat homes will quickly establish a hierarchy amongst themselves. This is a commonly accepted order status in the cat world and should not be interfered with by owners. In such a hierarchy one cat will take the top dominant position. This cat will then be known as the
'alpha-wolf' so to speak. The lowest cat on the totem pole is known as the pariah. This set up is normal and should not be interfered with.

Such a system is usually set up through several encounters of 'play fights' between the various cats in the home, quickly the hierarchy will be set up. This hierarchy can be seen throughout your cat's daily lives. You will notice your dominant cat being the first to eat, first to play, the
first to want and get your attention etc. The dominant cat will perch at the highest spot in a room (height equals respect in the cat world), while the other cats will then position themselves is descending heights.

Many shelters now-a-days actually have plenty of cat towers and various objects of various heights such that the cats can display their dominance while in the shelter.

Also remember that cats are creatures of habit. They like routines and low-stress environments. To them this established hierarchy is part of their routine and habit. If they are not allowed to do such they will get stressed and anxious. You should not try to go against this system.
Your dominant cat isn't being mean or bossy, just following his/her instinctual laws. Although it may be difficult at times, follow the hierarchy your cats have set up. Treat the dominant cat as the dominant cat, make sure to give treats or feed that cat first. Going against the system will generally cause the dominant cat to become aggressive in
an attempt to regain his/her role. Cats who feel their dominance or place in the hierarchy is threatened may also start to exhibit the following behaviors:

Spraying
Litterbox problems
Biting, or Scratching
Aggressive Behavior
Hissing

Hope this helps.

That article was quite interesting, although it created as many questions as it answered. Is the older animal usually the dominant one? Would it be the cat who was there first? If not, could a change in the hierarchy affect the behavior of the original cat? I am just trying to apply the thoughts of this article to my cats and see which one is the dominant one.

There really is no set rule on who is going to be the dominant one. It is all in that particular cats personality. I have young cats who are higher than the older. They usually just find their own places in the house. I have noticed though, that the cats with an insecurity usually need to be in the higher spots.

Well, I'd have to think that Squirt would be my dominant cat, although there are no clear cut signs. Joey just seems to be too mentally challenged to assume the role.