Thy Kingdom Come

At the beginning of time, there only existed two types of beings: The Elder Gods and the One Being. The One Being gained his power by draining that of the Elder Gods. Eventually the Elder Gods declared war on the One Being to save themselves. In the end, the Elder Gods created 6 weapons called the Kamidogu. When they used the Kamidogu,[clarify] the One Being split into many pieces, although its consciousness survived. The Kamidogu became lost in 6 different pieces of the One Being. Eventually, these pieces became the realms, and life began to grow inside them. There were 6 main realms: Earthrealm, Netherrealm, Outworld, Orderrealm (Seido), Chaosrealm, and Edenia, each with a representative Kamidogu which held the essence of each realm. The question was then asked of how realms could be combined. The Elder Gods decreed that the denizens of one realm could only conquer another realm by defeating the defending realm's greatest warriors in ten consecutive Mortal Kombat tournaments.

The Elder Gods watched over the realms, and governed the realms with untold wisdom; but one such Elder God, known as Shinnok, gave in to greed and the illusion of false power and wanted the new realm of Earth for himself; however, the Elder Gods had appointed the young God of Thunder known as Raiden to protect Earth. The battle between Raiden and Shinnok was fierce, sending Earth to its near destruction and plunging it into centuries of darkness. Raiden discovered that Shinnok entered the realm through the power of a mystical amulet. It allowed Shinnok to weaken the borders of a realm and therefore enter the realm without challenge and keep the Elder Gods from interfering. Forced to choose between destroying the budding Saurian civilization or to give Earthrealm to Shinnok, Raiden chose the former and stripped the amulet of Shinnok's possession and with the aid of Elder Gods banished the fallen Elder God to the Netherrealm. Raiden buried the amulet deep with the mountains of Asia and created a massive temple to house the amulet and appointed four guardians to serve as the protectors of the amulet. These guardians represented an element that make up the realm: Wind (Fujin), Earth, Water, and Fire. As long as the amulet remained on Earth, Shinnok would remain trapped in the Netherrealm..
At some unknown point in history an emperor called Onaga ruled the realm of Outworld. Onaga was the first Emperor of Outworld, uniting an otherwise divided realm. He began to conquer other realms, merging them to add that realm's power to Outworld and expand his ever-growing domain. Onaga's secret to victory was his undefeatable and seemingly invincible army. Onaga's heart gave him the ability to raise the dead, allowing him to revive his dead soldiers over and over. However, Onaga wished to live forever; using the last dragon egg, his followers formed a spell that would transfer his body into the tiny dragon inside and with it, be granted eternal life. It was at this point Shao Kahn, who had been a trusted advisor at Onaga's side, decided to strike. Onaga was poisoned, and with Onaga gone, Shao Kahn took control. However, unlike Onaga, Shao Kahn was not able to rule Outworld as a united realm.

Like Onaga before him, Kahn sought to expand his domain and his power through conquests of other realms. He attacked and conquered many smaller realms, slowly building up power over thousands of years. Eventually, he built up enough strength to take on another realm equal to Outworld's size, to gain even greater power, Edenia. To conquer Edenia, Kahn had to win the sacred tournament protecting the realm, and if he succeeded, it would allow him to merge the two realms. Despite the Edenian warriors' best efforts, Kahn eventually won and Edenia was conquered. The ruler of Edenia, King Jerrod, was murdered; Kahn took his wife Sindel as his queen and adopted their daughter Kitana as his own. However, Sindel could not bear the thought of being Kahn's queen and committed suicide..
A realm may declare Mortal Kombat on another realm if they wish to invade it and conquer it. Once one party declares Mortal Kombat, the other party may not refuse. A tournament ensues, where the combatants will be knocked out until the reigning champion does battle with the challenger. Once defeated, a single Tournament victory is added for the realm. Once that realm earns ten Tournament victories in a row, they earn the right to invade the losing realm. This is the only 'legal' way for a realm to invade another, and any violation of this rule is seen as treason against the Elder Gods. The reigning champion will have their aging suspended by the Elder Gods until the next tournament.