The "Expand Borders" quest doesn't work very well for Underworld. It doesn't fit thematically, since Underworld doesn't seem to really have/care about borders. From a practical point of view, we have to journey much further to find an appropriate hex, and since we can't just claim a neutral territory, we have to offend another nation right off by taking one of their hexes (not great for a nation trying to act as neutral mercenary types).
Perhaps underworld could have a different quest in it's place? Something like "trade cards with another player" or something else similarly fitting with Underworld's themes of neutral mercenaries and traders.
It's not a big deal if we can't of course. But it would be nice.
EDIT: Just noticed your reply in the Day 1 topic. I still think it'd be nice if the supposedly mercenary UW didn't have to offend a potential employer just to complete a basic quest, but at least the +1xp is a good acknowledgement of the extra difficulty.