[jason taylor]

Underground combat wasn't a big part of warfare in the pre-gunpowder era. It isn't now for that matter. The best analogue would be urban warfare as it takes place in buildings. But most descriptions of that seem to be post-1900. For some reason it is hard to find famous examples of cities fighting on once the walls were breached. That would make sense if it was to avoid a sack, but often sacks weren't resisted when they could well have. The best example I can think of of pre-1900 urban warfare was Sarragossa. In any case it is hard to think of example's with medieval weapons.

As I said, urban warfare is the closest analogue. Actual underground warfare is usually an addendum to siege warfare and as such has been known for ages. But this form wouldn't be as elaborate as it would be if dwarves actually existed.