The Empire is a nation in Minecraftia, currently hunting down Grayson after he recovered the Dragon Egg from the ruins after the Empire Civil War, in Emerald City when the Eastern Empire and Western Empire merged.
The Empire appears to be a central government somewhere to the north of the Badlands. This is shown in how they appear to have the manpower needed to chase Grayson, and how their currency seems widely adopted. This currency includes Shillings, Florins, Sovereigns, and Marques. It also includes Rubies and other treasures.
The Red Keep is the official entrance to the Empire, according to Drake, who says that's what he's always heard. There are other ways to enter the Empire, however, according to Grayson.
According to both Drake and Grayson, the centre of the Empire is the best place, and Drake has heard stories of the great cities there, which were confirmed as true by Grayson, who had actually gone there. It is known that Grayson actually had a family there, in a city named Emerald City, which presumably is a major city of the Empire. However, his house was burnt down, and his family executed when he stole the Dragon Egg.
The Empire are known to build camp settlements inside the Badlands, close to their border, such as the one nearby the Red Keep. The camps have been known to get abandoned occasionally. They consist of tents, wooden fortifications and campfires.
The Empire's primary fighting force seems to consist mostly of mercenaries as opposed to any sort of standing army. Grayson, under the Western Empire, was named commander of the Imperial Army and right-hand-man to the Emperor. The Empire is also known to field a fleet of airships, consisting of both hot air balloons and larger, more blimp-like airships.
The Empire is known to have several museums, that will pay handsomely for ancient artifacts, with Mia having presumably done business with them several times in the past, despite her bad history with the Empire.