The Crossline is the boundary of the Holy Country - Belintar never claimed the lands to the north of the Crossline (he certainly possessed the resources to conquer the troublesome Quivini if he so chose). The Volsaxi were rebels against Belintar; Sartar was an independent principality. To annex the Volsaxi into the Kingdom of Sartar would mean direct conflict with Belintar - a very high risk proposition (and one that would likely result only in a Lunar triumph).
Jeff
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