Alshanai Rift

The Alshanai Rift is a region of space that borders the Klingon Empire and the Federation. The planets within this sector of space were subject to pirate raids conducted by Orion pirate raiders whose services were bought by the Klingons. This was because the Klingons wished the worlds to abandon thei allegiance to the Federation and join the Empire.

(TOS novel: The Final Reflection)