Ninja Gaiden II: The Dark Sword of Chaos, known in Europe as Shadow Warriors II: The Dark Sword of Chaos, is a side-scrolling platform game developed and published by Tecmo for the Nintendo Entertainment System (NES). This is the second installment in the Ninja Gaiden trilogy for the NES and was released in North America and Japan in 1990, and in Europe in 1992.

The events in Ninja Gaiden II take place one year after the events in the first Ninja Gaiden game. It is about an evil emperor named Ashtar who, after hearing of Jaquio's defeat, devises a plan to take over the world and engulf it in darkness through an evil sword called the Dark Sword of Chaos. A U.S. Army agent named Robert T. Sturgeon recruits the game's protagonist Ryu Hayabusa and tells him that he is the only person who can stop him. The game received praise in previews from Electronic Gaming Monthly and Nintendo Power and continued to receive high ratings and coverage, being nominated for several awards from Nintendo Power in 1991. Reviewers said that visuals and controls of Ninja Gaiden II improved over its predecessor while maintaining a high level of difficulty for players; the game was criticized for having a more generic and predictable plot. The game maintains lasting appeal among players, with one reviewer saying that Ninja Gaiden II is "a challenging experience the likes of which gamers in the 8-bit era lived and died for".