The undead is also known as The Forsaken or The Undead Forsaken. They are intelligent beings who broke away from the scourge and took control of Lordaeron. Lordaeron was destroyed by Arthas Menethil during the Third War. They were led by Sylvanas Windrunner, who was the former Ranger-General of Quel’thalas and the founder of The Forsaken.
The Forsaken is a diverse faction that includes many races at their biological core. They have shared goals and loyalties, so they assumed their racial identity as Forsaken. The Lich King’s grasp on his armies faltered after the Third War, once this happened the undead broke free of his will. Some of them were tormented by memories of what they’ve done when they were Arthas’s mindless Scourge agents.
They became hated and everyone in Azeroth sought their destruction. The ones who did not become mad realized this. They rallied together by Sylvanas. She was defeated during an attack on her kingdom and became a scourage Banshee, Sylvanas regained her freedom from the Lich King.
The Forsaken had a new queen and they were independent. They would now be called The Forsaken. Establishing Undercity beneath the ruins of Lordaeron. Some Forsaken feared Sylvanas, while others valued the security she offered them. They would soon find a purpose to their existence through the Queen’s desire to destroy the Lich King for what he did to them and her.
No Longer Scourge?
Sylvanas and her people were no longer scourge, but humans wanted to eradicate all undead and had threatened the scourge. The Banshee Queen sought allies for her nation as well as for a means to further her own goals. The Tauren proved to be the most promising contact for her and her people. Archdruid Hamuul Runetotem saw potential for redemption in her people, even though he knew about the sinister nature of the Forsaken.
Joining The Horde
The Tauren convinced Warchief, Thrall, to forge an alliance with the Forsaken. Thrall had some reservations about doing so, but gave him. The Forsaken had a higher chance of victory against the Lich King, and the Horde would gain a foothold inside of Eastern Kingdoms. Lordaeron previously was destroyed by a scourge army when Prince Arthas commanded them, this became the perfect threshold for the Undead race.
There were a ton of humans killed during the Lich King’s campaign to remove all the living from Lordaeron. The kingdom’s fallen were risen into undeath as Scourge minions. They were forced to wage an unholy war against everything and everyone they loved.
Some believe that Lady Sylvanas is nothing more than a pawn in the Jailers game, as this has also been canon. Let’s face it, this is Blizzard we are talking about, things in lore change frequently. It was shocking to find out this had been planned since Wrath of the Lich King, so you tell me, what do you predict will be Sylvanas’s ultimate fate in Shadowlands, as well as her former people?