The Horde Wars was the name given to the major conflict fought between the Kingdom of New Lordaeran and the Horde Kigndom of Durotar. The war was named after the Orcish army, which was also known as the Horde. These armies were two of the largest ever pitted against each other in history, and the fighting between them rapidly spread to countless inhabited areas of Azeroth and Draenor. Both sides scored significant victories over the other, and at different times during the war either seemed likely to triumph. The deaths of Krush and Olgik, coupled with the order to slughter the Paladins and the disbanding of the Horde brought an end to the fighting. At the time, it was the largest conflict to date.
Unbeknownst to most of those involved, the conflict was started, maintained and eventually ended by the Death Knight Methis, whose ultimate goal was the transformation of the Kingdom of New Lordaeran into the Empire of New Lordaeran with him as Emperor and dictator as well as the eradication of the Paladin Order. The conflict would lead to the Order of the Death Knights controlling the dominant Azerothian government.
Although the Horde Wars officially began 22 years after the Battle of Mount Hyjal at the Battle of the Canyon, their origins could be found ten years prior, during the siege of Orgrimmar by the Undead Scourge. The aftermath saw the appointment of Methis to the office of Regent of New Lordaeran. He promised to bring an end to the corruption that had so often plagued the Royal Court. The first few years of his tenure saw very little to fulfill that promise, however. The demilitarization of the Scourge was viewed by many as little more than a slap on the wrist, and Kel'Thuzad, leader of the Scourge, managed to avoid any serious charges against him due to his role in the Orgrimmar conflict despite opposition from numerous human, elven, dwarven and mage courtiers.
During this time, Methis, in his alter ego of a Death Knight, had contacted the experienced Paladin Gaius. Having lost his follower Mallus during the Orgrimmar conflict, Methis was in need of a new follower and Gaius, whose own faith in New Lordaeran had been shattered following the Battle of New Dalaran, seemed the perfect one to mold.