Traditionalist Cats

Traditionalist cats are cats who embody the Law of Cat Heavens. In doing so, they are ensured a place in that afterlife and are sometimes able to access celestial blessings.
Traditionalist Cats commune with the Heaven of Stars, a facet of the Cat Heavens that embodies tradition, continuity, honor, oath-making, and stubborn perserverence. The Heaven of Stars demands that all Traditionalists follow the Star Code, and many Traditionalists wage religious war on any cats who do not follow their interpretation of that Code. Traditionalists can commune with the Heaven of Stars through sacred sites consecrated through ritual worship. It is through this communion that Traditionalists remain consistent across centuries and continents: they are magically bolstered against any kind of change.
The Heaven of Stars demands that all cats sworn to them obey their code:

• All cats must organize into Clans, Nations, Tribes, Bands, or Peoples. Each group must have defined territory and membership, without overlap.
• All cats must be loyal to their people over all others.
• All peoples must respect the territory of others unless seized through righteous and legal war.
• All peoples must be divided between Elders, Young, Apprentices, and Citizens.
• The Apprentices must feed the Elders and Young before themselves.
• There are age requirements for social advancement
• There is a re-naming ritual for becoming a Citizen
• All Nations must elect a lifelong ruler with a Deputy heir
• All neighboring Nations must meet regularly for a holiday of peace
• Boundaries must be marked and enforced through ritual and ritual battle
• Young must be protected even if they are not of the Nation
• Fighting must be for dominance, not killing; full lethality is to be avoided unless necessary or unless that Cat is not a Traditionalist
• All Traditionalists must refuse the rule of humanoids

This code was given to them by The Hidden One and is taken deathly seriously.
Traditionalists are usually rural cats, to better avoid being ruled by humanoids. They are often proselytizing in their religion and will actively integrate any non-traditionalists who join their number. There are exceptions to both of these rules: there are urban Traditionalists and there are religiously syncretic ones. 
The original structure given by The Hidden One was an intentional mimicry of the 'Warrior Cats' book series, but it is worth noting that Cat Traditionalists do not need to adhere to any lore or rules of that series. Local groups of traditionalists approach the Code and Heavens differently and the system has subtly mutated since its inception thousands of years ago.