Isolation could be achieved around multiple star systems, too - although probably not with a chain of asteroid outposts so few that a random selection only shows us numbers 1 through 8, rather than, say, 23909588 through 23909596.
Would the goal of the isolation be withering of the empire locked inside? This might work with a single star system (it probably takes interstellar trade for any civilization to evolve to such a high level that they can ultimately sustain themselves by exploiting their own star system only), but not with a "prison" or "reservation" encompassing dozens of star systems.
Or would the goal simply be postponing of further conflicts by providing a formal excuse from attempts to exploit the same resources? The RNZ might be of mutual benefit in that case; even if only one side had the actual guardtowers, the other would also enjoy the symbolic protection of the barbed wire, until time was ripe to have conflict again.
The invisible ship might have been intended as the WWI tank, a novel means of breaking through the RNZ, after which the war could proceed with conventional means and the cloakship would become useless. In such a case, the ship probably wouldn't even need a warp drive. But if the RNZ always was more a symbolic than a concrete obstacle, then the cloakship probably was designed as a means of waging the actual war and triumphing over Earth this time around.