Samarkand is the land that lies to the east and north of Tamriel in Age of Industry.
In 5E 566 an alliance between the Argonians and the Khajiit was formed, in order to escape from the Empire's yoke. This alliance was effective enough to throw out the Empire from their provinces, and thus the lands of Samarkand were formed.
This alliance went on to gain many other lands, both from conquest and diplomacy. By the sixth era Samarkand had become a large and powerful kingdom, perhaps large enough to rival the Empire itself.
Samarkand encompasses the old political borders of Morrowind, Skyrim, Black Marsh, Elsweyr, and the Nibenay Basin of Cyrodiil.
Samarkand is ruled by both a king and a queen. Because it was originally formed by the Argonians and the Khajiit, Samarkand is ruled by both races. An Argonian king will rule alongside a Khajiit queen, for example, and the next generation a Khajiit king will rule with an Argonian queen.
Both monarchs have fairly equal power, and any decisions must be reached by both monarchs together. The king and queen are not actually married, but each one has children that continue the lineage.