Lordaeron, once shining bastion of humanity. Now, only a pale shadow lying in the ruins of its former self. Who is the true ruler of Lordaeron these days, when the bloodline of House Menethil is all but gone? To whom does Lordaeron belong? Who is here the usurper, and who the legitimate heir of abandoned bloodied throne?
The throne room to this day still echoes of heinous betrayal Arthas committed so many years ago. The halls still echo of patricide that took place when the prodigal son came home at last, from what seemed as a madman's chase of shadows.
We have three major figures in play here. Arthas Menethil who is now dead, Sylvanas Windrunner, and Calia Menethil who is for all we know either lost or dead. We know, that Calia was two years Arthas's senior, yet the one who would be next king was Arthas. That is not to say that Calia would in no case inherit the crown, it just means she was the last pick, even though she was the eldest child.
Now, had Arthas not done, what he had done, one day he would become a king, have his own children and his sons would probably rule after he died. Yet Arthas was not a patient son. He killed his father, only to rule. And once he ruled, he killed everyone. All the nobles, peasants, merchants, guards. Nobody was safe before Arthas and the commands given to him by, in eternal ice encased, Lich King.
Now, in our world getting the land in that case would be no issue. Let us say that plague devastated a kingdom, actually managed to kill all the populace. What would happen, is that neighbouring, or ally countries would claim that territory for themselves. Which in practice sounds fine. You either claim that land and try to profit from it, or you let it go to waste.
The problem is, that while yes, all the citizens of Lordaeron are dead, they are not your usual kind of dead. The usual dead stays silent laying in their coffins. Lordaeron's Forsaken on other hand are still kicking. They are all driven and motivated. They have no reason to just lay in their overdue graves and never speak again.
Not even the insanity argument is of help in their case. Those that lose their sanity are broken, their will bent by the Lich King. The rest, determined, motivated, full of resentment and wish to inflict as much pain as possible on the world, are Forsaken. Former citizens of Lordaeron, and Quel'Thalas until Arthas slaughtered them. They are sociopaths, nobody can refute that, yet they are not insane.
After the defeat of Burning Legion on the Mount Hyjal, Arthas styled himself as King. Even after his father's death at his own hands, Arthas continued to use the title of a Prince. But that did not last for long. Soon, his powers started to wither. Sylvanas, now the banshee, regained her free will. The others that once served her in life, continued to do so in their undeath. With the help of other undead she found her dead body and took control over what was until then but an empty husk.
Sylvanas ambushed Arthas. And she would have killed him if not for Kel'thuzad, one of the few remaining loyal servants of the Lich King. Nevertheless, Arthas escaped to Northrend, trying to save the Lich King from Illidan and Kael'thas. The Forsaken in Lordaeron regained their free will as Lich King's grasp weakened. And they, as one, swore alliegence to the Dark Lady, Banshee Queen Sylvanas Windruner.
She dealt with the remaining dreadlords with the help of Varimathras and Garithos, the human Grand Marshal who once sought to execute Kael'thas for accepting the help of Nagas in his defence of Dalaran against the Scourge. And after she recaptured the Capital, she had Garithos executed on the spot. Since then, Sylvanas first reinforced what she had of military and started dealing with the few renegades that still remained in Tirisfal, Plaguelands and Silverpine.
After the Burning Crusade, when her apothecaries perfected the new plague weapon, she joined the assault on Northrend. She wanted to see Arthas dead and she had no reservations about the means, only to see it through. Her majordomo had other plans though. Varimathras tried to use the situation in Northrend for his own goals. He wanted to summon his Master. One can only guess who could that be. Thus the Forsaken civil war started. At the end, Sylvanas with the help of Horde forces prevailed.
As seen from all this, Sylvanas is the only legitimate ruler of Lordaeron and Forsaken. Arthas is dead, and while Calia might by some strange luck be alive, in hiding, or something else entirely, she lost any chance for the throne of Lordaeron once Forsaken regained their free will. Sylvanas was the one who drove Arthas to exile. Sylvanas was the one to ensure Arthas died. Sylvanas was the one to deal with the betrayers from within her own ranks. And Sylvanas was the one who conquered Hillsbrad and started the expansion into Gilneas and Western Plaguelands.
At the end of the day, Forsaken, citizens of Loraeron proclaimed Sylvanas their Queen. We could say, that people of Lordaeron had their own revolution, where they overthrew the king and proclaimed their new Queen.
Even though there are some who survived all this, who escaped to Theramore or Stormwind, far more died and became Forsaken. Forsaken are the only one who get to decide who rules over them. They are independant nation, even though their nation is consisted of more than just one race. Even though humans once lived and ruled Lordaeron, humans of Stormwind, Stromgarde and other kingdoms, have no real claim over what we now know as domain of Forsaken.
And this is why words like reclamation of Lordaeron coming from Varian Vrynn sound so hollow. They were hollow back in the Battle for Undercity, and they are hollow even now, when Garrosh is defeated. From whom is he about to reclaim that land? From its rightful owners?