how can i stop my new cat from fighting with my others?

This is a very typical situation which I've gone through myself several times. As others have pointed out, it's basically a territorial thing and this sort of thing will continue until they all sort out the new territorial relationships. This can take six months to a year so don't make any hasty decisions about rehoming her. The standard advice on this is to keep the new cat separate in another room for a period of time so that they can get used to the smell of each other without actually having to encounter each other. But it will take time. The male cat is behaving in a territorial dominant way by sitting at the top of the stairs or by the door, he is controlling a route that all the other cats have to use. The new cat in attacking him is challenging his control and she is trying to take the top cat position away from him. Your female that has taken to sitting up in high places is also trying to hold a dominant place. In cat territorial language, the cat who holds the physically highest position is generally the dominant one. It's also easier to defend against attack which may be you female's main motive for sitting up high. One of my older famale cats usually lies at the top of the stairs where she is, as I said above, controlling a main access route and she is the dominant cat amungst my 5 cats. Even me big male will not challenge her and I've seen him sitting on the stairs rather than try and get past her. But he is a bit softie I have to admit.

very simple........ just kill her......... lolzzzzzzzzzz

I understand this must be a huge problem for you! It is not fun when your pets doesn't get along. I have no text book answer for you, unfortunately, but I have been in a similar situation. My parents had a cat and then they got a new one, both were female cats. The new one didn't like the old one much, and they were fighting. Mom always ran in between and stopped them from fighting. Now it is not possible to have them together. One has to be out when the other one is inside, and the other way around. Much of a hazzle for my parents.. However, I do think that if mom would have let them fight when the new cat came, then they would have fought and settled the "order" between them of who is the boss. Then they would have tolerated each other. I mean, that is how it is done in the wild in packs of animal. Obviously that is just my thought, I have no idea how it would have turned out if mom would have let them fought, and I don't know if that is of any help to you. It is just a thought :)

They will eventually get along. I have had cats for many years. Last one we had her by herself for about two years. We then were blessed with a three week old that someone threw off a bridge into the water, we could not leave it, so we took him home. They still fight from time to time, but they are also best friends now. They play together, clean each other, and sleep together. Just give them time to work things out.

It can take a couple of months for animals to get used to each other. I'm assuming that when you brought her in, (your new cat) You didn't do it slowly enough. If you just bring in a new cat, and just go... have at it... there is going to be a lot of fighting. Give it another month or so. Try to ease the tension if you can by isolating the animals when the house is empty. This usually needs to be done for the first couple of weeks after bringing in a new cat, but all I can offer you is time. If you can afford it get the feelaway cat desuers. This will relax the animals and plugs into the wall like a glade plug-in. they can be pricey and are sold in most vets offices or petsmart.

Cats are very territorial and do not like change. 3 weeks is not long enough. They may need up to a couple of months to be friends, and they will be friends. Eventually. Do not worry, and make sure to give them all equal attention because they are such jealous creatures. I have 5, one is the momma cat who wanted nothing to do with her litter once they came of age. It took her awhile to get used to the idea that the kittens were not going anywhere. I think it was a few months of the opposite of heaven but eventually she settled down about it.

I suppose they already have what they consider their territory and she is the usurper. She wants to establish her boundaries maybe. My Mother in law had 6 cats and they lived anywhere in the house that they liked which meant sometimes you would find one on the bookcase above your head or under a shelf in the kitchen . None of them fought but they weren't often together unless it was meal times. Maybe she needs a bit of a private space to feel comfortable in

My girlfriend has the same problem... she has got 3 cats, 1 cat (white) gets along with the black and the grey one, but the black and the grey one are always fighting eachothers... shes just keeping them in separate rooms and never leaves the doors open for the black and grey to meet... i would just throw one of the problematic cats away, i wouldnt change my lifestyle for some beasties.