In the first campaign of the game, Illidan's former warden, Maiev Shadowsong, hunts for Illidan and finds the serpent-like Naga who vow to "retake the surface world" from the Night Elves. Maiev later follows Illidan to a recently erected island and to a vault located within. It is revealed that Illidan Stormrage has gained the allegiance of the Naga, former night elves mutated by The Sundering, and obtained an artifact called the Eye of Sargeras from his tomb (in chapter 3 of the campaign), which grants him extraordinary power. Maiev Shadowsong, calls for the aid of Malfurion Stormrage and Tyrande Whisperwind to capture Illidan. Partway through the pursuit, Tyrande is swept away by a river while helping a group of blood elves to retaliate against the undead. Maiev convinces Malfurion that she died at the hands of the undead. When they finally capture Illidan, he explains that he planned to use the Eye to destroy the Lich King, ruler of the undead... much to Maiev's dismay. At this point Illidan's Naga Scouts discovers that Tyrande may still be alive. She was surrounded by water and undead settlements. Only Illidan and his naga can reach her (By water). The brothersStormrage work together in order to rescue her. Malfurion then pardons Illidan for his actions done with the Eye, but reminds him that he is still exiled. Illidan then flees to Outland (only know after the cutscene where blood elves met Illidan at Outland where he speaks of how he came to be).
The second campaign follows the blood elves, the last of the High Elves, led by their prince Kael'thas. They are given the job to fix watchtowers and defend them by a human leader named Garithos, who despises non-humans. He later discovers that Kael'thas was helped by the Naga and imprisons the blood elves for this. They are rescued by Lady Vashj, leader of the Naga, who leads them all to Outland. Once there they join forces with Illidan and conquer Outland, with promises of claiming magical energy to satisfy the Blood Elves' addiction to the arcane. Once Outland is conquered, Illidan's master - the warlock Kil'jaeden the Deceiver - finds Illidan and prepares to punish him for his failure to destroy the Lich King. However, Illidan convinces Kil'jaeden to give him one more chance, claiming that he was gathering more forces to assault the Lich King's Frozen Throne. The Deceiver lets Illidan's failure go, but warns him to kill Ner'zhul or face his 'eternal wrath.' The blood elf campaign is the shortest in Warcraft III, with only six chapters (seven including the secret mission).
The third campaign follows the undead, who have split into three factions. One is led by Arthas and is loyal to the Lich King and accompanied by the necromancers of the Lich, Kel'thuzad; another is led by the banshee Sylvanas Windrunner; and the third is led by three dreadlords and are loyal to the Burning Legion. The playercontrols Arthas' and Sylvanas' factions in the different chapters, opposed to the dreadlords' faction. The brothers are complaining that they haven't heard from Archimonde the Defiler, who was killed just about a week ago. Sylvanas asks Kel'Thuzad what happened to the Legion. The Summoner states that the Burning Legion took off after Archimonde was slain. The conversation is interrupted when Arthas [mounted on his prized horse Invincible] bursts through the gates and thanks the brothers for looking after Lordaeron while he was gone. One of the brothers, Balnazar, says the Scourge is owned by the Legion. Arthas cleverly states that Archimonde's death was announced. The brothers retreat. After emptying the kingdom of the remnants of the Alliance, Arthas prepares to travel to Northrend for an expedition there, but the 3 brothers trap him inside the castle, much to Kel'Thuzad's shock. Kel'Thuzad has no choice but to turn around and run away. Arthas manages to escape and is taken to a spot for rest by some banshees. Arthas is shot in the leg by Sylvanas for turning her and her people into banshees. Fortunately, Kel'Thuzad appears from the shadows and drive Sylvanas away. The poison wears off, and Arthas leaves for Northrend. When he and his forces get there, Arthas learns that he needs to defend the Lich King from Illidan, the Naga, and the Blood Elves' combined assault after having painful attacks and visions of the Lich King commanding him to the Frozen Throne. First they are given help by Anub'arak, the Ancient King of Azjol-Nerub. He knows the kingdom will be a shortcut to Icecrown Citadel. As they travel, they recruit the ancient blue wyrm, Sapphiron of the Blue Dragonflight (servant of Malygos the Spell-Weaver), into the undead Scourge. They then use the giant wyrm to smash other enemy forces that might counterattack.
Meanwhile, back in the subcontinent of Lordaeron, Sylvanas is lamenting over her being an undead, although she and her forces are permanently freed of Ner'zhul's grasp. Later, a demonic portal appears. Emerging through it is one of the Nathrezim, Varimathras. He offers Sylvanas to join the Burning Legion and rule the subcontinent and the Kingdom of Lordaeron. She refuses, much to Varimathras' displeasure. However, Sylvanas and her forces attack and corner him. He begs for mercy and joins Sylvanas's force, now known as The Forsaken. They then approach a stronghold held in the grasp of Detheroc, the oldest of the 3 brothers. They brainwash what's left of Garithos' forces, besiege the stronghold and free Garithos by killing Detheroc. Although Garithos knows Sylvanas might be one of the Scourge, she reassures him that she is free. Varimathras and Garithos argue over something out of subject until Sylvanas calms them. They then besiegethe kingdom and corner Balnazaar. Sylvanas orders Varimathras to slaughter him. He at first refuses, but is forced to attack. Garithos, driven by racism, orders them to leave, but Varimathras cuts his neck, causing him to bleed to death. Lordaeron is now the home of the Forsaken, who then join the Horde after learning Thrall's shamistic powers.
Arthas, Anub'arak and the undead forces are at the right place: Azjol-Nerub. However, a small group of dwarves have the front gates shut. Arthas orders Sapphiron to attack. He flies in and spits a bolt of frost at the gates, which fall to pieces. Arthas wishes to take Sapphiron with them, but can't because the confines of the dark earth isn't a place for Sapphiron, who flies to the other side. They then meet with Bealgun, who tells Arthas and his forces of the horrors that dwell deep within the kingdom, that they be careful. Anub'arak realizes Bealgun's stories are true. They then encounter a gigantic Forgotten One and rip it to pieces... but more Faceless ones show up and chase them off. Arthas senses the ceiling is about to cave in and darts to the other side just in time... Anub'arak simply smashes through the boulders with his massive bulk. They eventually find the exit and get some rest before going on.
After a fierce battle between Arthas' undead forces and Illidan's, Illidan appears to be slain and Arthas is able to reach the Lich King's Frozen Throne. Once there, Arthas shatters the ice-prison that held the Lich Kings remains, releasing him. Arthas dons the Lich King's helmet, joining their souls into one ultra-powerful being: Arthas, the new Lich King.
The separate RPG-style campaign follows the Horde defending their land and building up a new kingdom called Durotar by Thrall in the name of his father Durotan. The main characters of the campaign are Rexxar, the beastmaster/adventurer - he admires the orc art of war - the private shadow hunter Rokhan, Cairne Bloodhoof, the tauren Chieftain and, optionally, Chen Stormstout, the Pandaren brewmaster. After defending Durotar from a series of lesser threats, Rexxar learns that a force of humans from the island of Theramore, led by Admiral Daelin Proudmoore, plans to invade Durotar. Admiral Proudmoore is unwilling or unable to accept a truce between the Horde and the Alliance despite their combined armies having defended the World Tree in Reign of Chaos. The orcs invade Theramore (aided by a guilty Jaina Proudmoore) and slay the Admiral, replacing him with his daughter, Jaina.
