As opposed to the heavily Oriental themes of Mortal Kombat and Mortal Kombat II, MK3's theme is much more Western contemporary. The game's stages are set in modern locations, three of the characters are robots, and traditional character designs (such as Sub-Zero's or Kano's) have been dropped or modified in favor of modern replacements. The overall game has a much darker tone then its predecessors, and uses a noticeable darker and less vibrant color palette. Characters are now heavily digitised (as opposed to the hybrid digitised/hand-drawn style of Mortal Kombat II.) Many of the game's backgrounds are now, for the first time, created using pre-rendered 3D graphics. This change is also reflected in the sound track, in which all Oriental motifs have been dropped in favor of modern instrumentation.
Fed up with continuous losses in tournament battle, Shao Kahn who had lost to Liu Kang in the Outworld tournament, enacts a 10,000 year-old plan. He would have his Shadow Priests, led by Shang Tsung, revive his former Queen Sindel, who unexpectedly died at a young age. However, she wouldn't be revived in the Outworld. She would be resurrected in the Earth Realm. This would allow Shao Kahn to cross the boundary lines and reclaim his queen.
When Sindel is reincarnated in Earth Realm, Shao Kahn reaches across the dimensions to reclaim her. As a consequence of his action, the Earth Realm becomes a part of the Outworld, killing billions instantly. Only a few are spared, as Raiden protects their souls. He tells them that Shao Kahn must be stopped, but he cannot interfere; due to his status, he has no power in Outworld, and Earth Realm is partially merged with Outworld.
Shao Kahn has unleashed extermination squads to roam throughout the Earth Realm and kill any survivors. Also, Raiden's protection only extends to the soul, not to the body, so his chosen warriors have to fight the extermination squads and repel Shao Kahn. Eventually somehow every human on Earthrealm comes back. (Wikipedia)