This map from the Glorantha sourcebook is very useful for getting an immediate feel for why the Lunar Empire largely ignores what is going on in Dragon Pass after the Dragonrise. See that white shaded area? That’s the White Moon Rebellion. Armed insurgents are less 40 miles away from Glamour and entire satrapies are in revolt.
And see the Voor-ash? They operate with impunity in Oraya and First Blessed. Raiders and bandits are at the outskirts of Raibanth. And what if the Voor-ash make a common cause with the White Moonies?
Now see all the way at the bottom of the map? That’s Dragon Pass with Furthest as an anchor.
What is blocking the Lunar expansion to the west of the empire? The Ban
As an aside, it is about 700 km from Glamour to Furthest. Now that might not sound a lot to people used to highways or ship travel, but that’s at least two weeks travel with plenty of remounts.
What is the best source for the White Moon Rebellion? The Glorantha Sourcebook. I don’t think GRoY, FS, or the Entekosiad give much or even any guidance.
Isn’t the White Moon uprising a generally peaceful, ideological movement? It was before the imperial authorities decided to kill many of the assembled leaders of the White Moon movement. That turned it from a “heresy” into an uprising.