The Total War Blog has word that the Rise of the Samurai DLC is now available on Steam, offering a new prequel campaign for Total War: Shogun 2, the strategy sequel set in feudal Japan. They offer a couple of trailer showing off its new content, and here's the description from Steam:

Set 400 years before the dramatic civil war depicted in SHOGUN 2, the "Rise of The Samurai" campaign is based on the Gempei War, a conflict between six legendary clans of the Taira, Minamoto and Fujiwara families. It culminated in the first Shogunate, and the rise of the Samurai as the ruling class.