Speak fool : Arthas Menethil p2

Arthas met heavy resistance from the elves, rallied by Ranger-General Sylvanas Windrunner. Driving their forces before his undead army, he steadily pushed her people back in a swath of destruction towards Silvermoon. Sylvanas tried to warn the vast elven capital of the coming of the Scourge, but Arthas destroyed her camps and killed the Ranger-General. To make her pay for her perceived insolence towards him, Arthas corrupted her elven spirit, transforming it into a horrendous twisted form (a banshee) and enslaving her to the will of the Lich King, forcing her to slay her own people.
Arthas, along with the marching armies of the Scourge annihilated Silvermoon, leaving it in ruins. On the road to the Sunwell, he faced Anasterian Sunstrider, the aged High King of Quel'Thalas, and killed him with minimal struggle. Arthas then used the Sunwell to bring Kel'Thuzad back to life, reborn as an undead lich.

Destruction of Dalaran
As the pair travelled to Alterac, Kel'Thuzad explained the full extent of the "Second Invasion" and the plans of the Lich King and the Scourge. Kel'Thuzad was in Alterac to destroy a camp of Blackrock Clan orcs who had taken control of a demon gate, which the lich would use to speak to the demon lord Archimonde. The Scourge destroyed the orcs, and after Kel'Thuzad received orders from Archimonde, they set out for the powerful seat of the world's mages, the city of Dalaran. Archimonde instructed them to acquire the spellbook of Medivh, which would allow Kel'Thuzad to summon Archimonde into Azeroth.
Despite the Kirin Tor's valiant efforts to repel the invasion, the Scourge fought through their magical defenses and fortifications, killed the Archmage Antonidas and claimed the Book of Medivh.

Arthas and his troops repelled the mages' vast counterattack as Kel'Thuzad began the lengthy summoning of the demon lord. Once Archimonde arrived, he proclaimed that the Lich King was of no further use to the Legion, and Tichondrius was placed in command of the Scourge. Arthas was left to wonder what would become of him and Kel'Thuzad, but the lich replied that all was going as the Lich King foresaw. The pair disappeared as Archimonde took his revenge on the city, destroying Dalaran with a single powerful ritual.



Arthas was next seen several months later in Kalimdor, where Tichondrius was employing the arcane power of the Skull of Gul'dan. Arthas told the recently freed demon hunter Illidan how to claim the skull's powers as his own, whereupon he could destroy Tichondrius. Illidan agreed to his plan, and Arthas disappeared again.

Return to Lordaeron

Arthas confronts the dreadlords.
Archimonde left a trio of dreadlords behind in the ruined palace gardens of Lordaeron to ensure that the nation remained under control, and to watch over the cunning servitors of Ner'zhul. When the demon lord was defeated, however, they were not originally aware of it. This changed several months later, when Arthas returned to reclaim his throne. He threatened the dreadlords, who immediately fled, and then called Sylvanas and Kel'Thuzad to his side. Together they crushed the remaining human refugees in the area, who were led by the paladins Dagren the Orcslayer, Halahk the Lifebringer and Magroth the Defender. However, during the climax of the battle, Arthas had a painful seizure, and felt the Lich King calling out to him. Despite his diminished powers, Arthas fought on until all the remaining humans were killed.
Little did Arthas know that the Lich King's power had dwindled to the point that Sylvanas was no longer under his control. In secret, she attended a meeting with the three dreadlords, who told her that the Lich King's power was waning, and so the time had come to claim her vengeance.

Arthas was ambushed in the capital city, and was forced to collect what loyalists he could find and fight his way through the dreadlords' forces, which included the powerful abomination Bloodfeast. As he arrived on the city's limits, he was saved by a cadre of banshees, who told him that Sylvanas had sent them to see him safely away. However, as they neared an empty spot in the forest, Arthas received another vision from the Lich King, who told him he'd been betrayed. Sylvanas then appeared and shot him with a paralyzing arrow. Kel'Thuzad stepped in and chased her off at the last moment.

But the Lich King's mental cries pierced Arthas' mind - he was told to return to Northrend, for demonic forces (later revealed to be Illidan and the naga) were working to destroy the Frozen Throne and end the self-proclaimed king's reign. Immediately, Arthas prepared his fleet and set sail for Northrend, leaving Kel'Thuzad behind to watch over Lordaeron.

Escape to Northrend

Arthas holding Frostmourne.

Arthas activates the obelisks.
Three weeks later, Arthas landed upon the familiar coast of Northrend, and unexpectedly found himself being attacked by blood elves led by Kael'thas, hungry for vengeance at their kingdom's destruction. Arthas was unexpectedly saved by a large Crypt lord who introduced himself as Anub'arak, the former king of Azjol-Nerub. Kael'thas warned that though the preliminary scouting force may have fallen, their main army would not be so easily defeated, before teleporting away to safety.
Arthas worried that he may be right, and that they would never reach Icecrown Citadel before Illidan, but Anub'arak thought differently. He suggested that they delve into the shattered kingdom of Azjol-Nerub, using the underground passageways to beat Illidan to the Glacier. Seeing little other choice, Arthas agreed.

Anub'arak suggested raiding the hoard of Sapphiron, an ancient blue dragon and servant of Malygos, and equipping themselves with the dragon's treasures. Not only did they slay the dragon, but Arthas used what power he had left to raise Sapphiron into a powerful frost wyrm.

Race to the Frozen Throne
When he came to the doors of Azjol-Nerub, Arthas found himself being fired upon by dwarves, who revealed themselves to be followers of Muradin who had remained there when their leader appeared to die. Now, they were led by Muradin's underling, Baelgun Flamebeard. Leaving Sapphiron outside, Arthas battled through not only Baelgun's dwarves, but also the nerubian survivors, as he delved into the broken Spider Kingdom. Anub'arak's aid was invaluable, as he circumvented many traps which would have cut Arthas' stay fatally short.
As Arthas Faced Baelgun, the dwarf warned that the shifting earth had released an ancient evil from below the kingdom. As Arthas and Anub'arak delved deeper into the kingdom, that evil became apparent - the Faceless Ones, a powerful, vicious race thought only to exist in legend. Arthas and Anub'arak even managed to defeat the incredibly powerful Forgotten one.

As they made their way to the Upper Kingdom, an earthquake collapsed part of the passage they were in, separating Anub'arak from Arthas. The young king had to rely upon his wits to see himself through several daunting booby traps before Anub'arak dug his way to Arthas. Once reunited the Crypt lord complimented the young Death Knight, saying he now understood why Ner'zhul had chosen him as his champion. As they climbed out of Azjol-Nerub, the Lich King contacted Arthas once again, and explained that he was losing his power, because the Frozen Throne had been cracked, and energy was seeping from it. Ner'zhul replenished Arthas' powers, knowing he would need them in the coming battle.

When they finally reached the surface, they immediately had to contend with Illidan's forces. Vashj's naga and Kael's blood elves were there to contest Arthas' minions at every turn. Arthas, with Anub'arak's help, battled his way through their forces and magically activated the four Icecrown Obelisks around the glacier, opening the doors to the Frozen Throne. However, Illidan was waiting for him.

The Lich King triumphant

Arthas fighting Illidan at the base of Icecrown Glacier.

The Lich King on his throne.
After a short but intense battle, Illidan inadvertently left himself open and Arthas took advantage of it, slicing open the demon hunter's chest with Frostmourne. Illidan collapsed in the snow, as Arthas turned towards the doors of Icecrown. Before he walked away, Arthas warned Illidan to leave Azeroth and never return.

Arthas entered the hollow glacier and beheld a winding pinnacle chained to the ice. As he strode up the stairs towards his destiny, the voices of those he had forsaken flooded through his mind. He heard Muradin Bronzebeard, Uther, and Jaina calling out to him, yet he ignored them, continuing his ascent. Finally, he reached the pinnacle and before him he saw an icy cask. Inside was a suit of armour, arranged as if seated on a massive throne. Now only one voice spoke to him - the rasping whisper of Ner'zhul:

"Return the blade ... complete the circle ... release me from this prison!"

With a great cry of strength, Arthas brought Frostmourne to bear against the Lich King's icy prison and with a haunting scream, the Frozen Throne exploded, and shards of the crystal scattered on the ground. With Ner'zhul's thorny helm at his feet, Arthas leaned forward, picked it up, and placed the unimaginably powerful artifact on his head.

"Now," Ner'zhul's voice echoed within his mind, "we are one!"

In that moment, Ner'zhul and Arthas' spirits fused into a single mighty being, just as the Lich King had always planned. Arthas as a single being ceased to exist, now one half of one of the most powerful entities Azeroth had ever known, the new Lich King.

Lich King of the Scourge
Main article: Lich King

Arthas dies in the arms of his father's spirit as Tirion Fordring looks on.
While he dreamed, Arthas banished his humanity and suppressed Ner'zhul's spirit, allowing him to become the dominant personality of the Lich King. [2].
As the Lich King, Arthas instigated another Scourge invasion of Azeroth, provoking a counteroffensive in Northrend by the Horde, Alliance, Argent Crusade, and Knights of the Ebon Blade. In doing so, he lured powerful heroes to Northrend and placed many challenges before them, seeking to weed out the weak and make the strong question their own morality. He planned to raise the world's greatest fighters as his new champions, and use them to spearhead attacks on their homelands, in a reflection of his own journey. [3] [4]

Death
His plan nearly succeeded when a group of adventurers led by Tirion Fordring finally ascended to the Frozen Throne and did battle with him after Horde, Alliance and Ashen Verdict forces assaulted Icecrown Citadel. The Lich King froze Tirion in a block of ice, and in the middle of the battle, he suddenly killed the adventurers in one single mighty blow. Ultimately, the Lich King's plans were foiled when, just as he was about to raise them all into undeath, Tirion freed himself and destroyed Frostmourne with the Ashbringer, releasing all of the souls inside, including Arthas's soul. The Lich King was severely weakened, and Terenas resurrected the adventurers who defeated him alongside Tirion. As he lay dying, comforted by the spirit of his father, Arthas asked if it was over, to which Terenas replied "At long last. No king rules forever, my son." Arthas said that he saw only darkness before him, with his eyes rolling back and his hand falling lifelessly to the ground.
Tomb
There is no official information, but a new, large tomb inside the new Stormwind graveyard is believed to be Arthas' tomb, since it has the Lordaeron crest on it, and most major characters from Lordaeron have set resting places and / or monuments already.