The basic set-up of the Warriors books is that there are four clans of feral cats living in the forest. Repeatedly, they're put into positions where they have to work together, despite their rivalary (and all are ruled over by StarClan, the spirits of their ancestors), and they have shared history all the way. In the second series, they nearly all join in order to make a journey together when the forest is razed for a superhighway. There are cross-clan friendships, and generally mutual respect for the leaders (all of whom are supernaturally endowed with the traditional nine lives, naturally).
But at the same time, it's repeatedly stressed that there need to be four clans, and that attempts to abolish the four-clan system--its rivalries included--are only made by evil cats. Good cats work together when necessary, then return to their clans when the danger is over, and value their clan traditions and loyalties. The evil cat of the first series displayed his evil most prominently in his forcible joining of two of the clans, and use of intimidation tactics to try and force the other two to capitulate. During a major battle, the hero, Firestar, goes to StarClan and asks for help in winning, and he says that it's because the cats need to be reminded that there have always been four clans in the forest--StarClan corrects him... but only to say, "No, there have always been five." At another point, he makes the observation that "the lines that divide us are also the lines that join us," giving the impression of seams more than sunderings, despite the often violent clashes.
So... what is the political message coming out of it?