because that section of tau-31 is actually under BARF| control.
the gate/lane section of tau-31 is under KNF control
BAF| is trying to encircle KNF from the BAF controlled area
the lore states that BAF| is current winning in tau-31 but losing in leeds
that and they would have to deal with fighting CR/OC who do not want to see KNF entering
note that kusari has easy access to tau-23 using kyshu
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but thats just the story, if i was KNF i woulda just blown up the station to halt BMM's mining operations altogether
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also nobody said the kusari emperor was smart
the main reason is probably this: CR would side with BAF against kusari in tau-23. though BMM has a bad reputation, it is only a corporation, if KNF wants to bring thier military, its a huge threat to CR
that, and KNF would still suffer problems with BAF attacks, and it cannot fight a 5 front war.
So if KNF defeats bretonia, they can take out CR and IMG singlehandedly in tau-23