Board Thread:Skyrim/@comment-11344160-20160205154012/@comment-1600847-20160914180055

Blademaster Jauffre wrote: How much evidence do I need to gather? Evidence that isn't ambiguous.

The part you quoted from Ice and Chitin doesn't state that those Imperials are part of an invading force, nor who the Nords that they're fighting are.

Just because the High King agreed to join the Empire doesn't mean all his Jarls did, naturally. This "Danstrar" could be a rebel Jarl that's being fought after Skyrim became part of the Empire. The Imperials could be part of the local legion garrison sent to fight him.

But we don't know, because the book is ambiguous.