You’ve brought a new cat home to keep your present cat company, just like I did five years ago.  Instead of making friends, they’re fighting! Cat fights are often turf wars over resources. Debra Horowitz, an Animal Behaviorist from Missouri suggested spreading water bowls, food dishes and litter boxes around the home. Both of my cats have separate food dishes and litter boxes. You can think of this situation like having college room mates. Sometimes you have college room mates that you like and some times you have college room mates that you don’t. Depending on how much you have to run into them will determine how harmonious it will be where you live.  Look for the triggers, fighting is treatable with training. Teach each cat to associate good things with the others presence.  Over time, the contentious cats will likely call a truce. So if your cats are fighting over everything, even their cat scratching post, it’s time to start paying attention and stop the fighting.