Board Thread:Lore Discussion/@comment-24372248-20140417001838/@comment-13446185-20140417160027

Here are two quotes that sum up what happened;

"Even Tiber Septim, it was said, thought twice before conquering Black Marsh for his new Empire. The borders of the province fell easily to his forces, but he wisely decided to avoid the strategically unimportant inner swamps, and thus met with little resistance."

-Pocket Guide to the Empire, Third Edition: Black Marsh

"Resdayn was the last of the provinces to submit to Tiber Septim; like Black Marsh, it was never successfully invaded, and was peacefully incorporated by treaty into the Empire as the Province of Morrowind."

-A Short History of Morrowind