Ulug Ulus' is a vast Mongolian state better known as the 'Golden Horde'. It's part of a bigger empire, but among all the Mongolian states, it may be the most ambitious and fearsome.
It was founded after the great Genghis Khan divided his empire amongst his sons. When Genghis' grandson, Batu, became the leader of the Horde, he took his army westward and conquered many lands. He went as far as Poland and Hungary, fought successful battles at Legnica and Mohi, and even tried to besiege Vienna.
The next ruler, Berke, went even further, demanding the submission of the king of France. The Mongols then kept raiding Europe and the Byzantine Empire over the years, essentially subjugating many of the local rulers to the Khan. Meanwhile, in the East, they managed to conquer China, and travellers say that they rule it to this day.