Read the tension before it turns into a fight
Cats in conflict rarely start with a brawl. The earlier picture is a cat who waits on the stairs until the other passes, a cat who stops using a favourite chair, meals eaten in hurried gulps while glancing up, or one cat pointedly sitting in a doorway while the other pretends to sleep. Staring, blocking and silent displacement are a cat's way of arguing without injury, but a home where one cat always yields is not a peaceful home, it is an unequal one. Note which rooms, times and resources trigger the stand-offs, because tension that clusters around feeding or the litter tray has a different fix from tension that erupts in evening play hours.
Spread resources so nobody has to compete
The single most effective change is duplication with distance. Place litter trays in more than one quiet spot, water in a different room from food, and feeding stations far enough apart that each cat eats without seeing the other mid-meal. Add perches and beds at different heights and in different rooms, so a cat who is chased from the sofa has somewhere equally good to land rather than a floor-level exile under a table. Scratching posts near resting areas matter too, since scratching is how cats leave reassuring scent marks of their own. When every essential exists twice and neither copy sits in a dead end, the reason for guarding disappears.
Remove the ambush points in your layout
Walk your home at cat height and look for traps: a litter tray tucked in a corner with one way in, a hallway where two cats must pass nose to nose, a bed behind a door that another cat can pin shut by lying against it. Move trays so a cat using one can leave in two directions, shift furniture to widen pinch points, and add a shelf or box mid-corridor to break a head-on meeting into a detour. Vertical routes help most of all, because a cat who can travel along shelves and cupboard tops crosses the room without ever entering a rival's ground-level path.
Rebuild goodwill with scent and parallel play
Once the layout stops forcing contact, rebuild the relationship in small, safe doses. Feed the cats on opposite sides of a closed door so each links the other's smell with dinner, then progress to a cracked door or a screen as calm holds. Swap blankets between beds every few days so scent mixes without a meeting. Play with both cats at the same time in the same room, one wand toy per person at opposite ends, ending before excitement tips into chasing. If one cat came home recently from a vet visit smelling strange, keep the pair apart for a few hours and reintroduce gradually, since unfamiliar scent is a classic trigger for a sudden feud between old friends.
When tension needs outside help
Seek veterinary advice if a cat who was relaxed becomes irritable, hides, over-grooms or stops eating, because pain and illness often surface as hostility toward housemates. A behaviour professional is worth consulting when fights draw blood, when one cat is too frightened to reach food or a tray, or when weeks of layout changes bring no softening. Keep notes on incidents, times and triggers to hand over, since patterns are hard to see from inside the home. Sharing that reset work helps it stick, and KinsLe Care Teams lets your household divide tray checks, station refills and parallel play sessions per cat, with each finished job marked by a timestamp so nothing slips.