The Warning is the starting cinematic of the Human campaign: The Scourge of Lordaeron. The short movie features a meeting of the Alliance council with King Terenas, they discussed about Lordaeron's problems like the orc uprising in southern Lordaeron and the misterious plague, then The Last Guardian, Medivh, appears before the Alliance council. Medivh tries to warn King Terenas about the coming of the Legion and the Scourge, but the king didn't pay any heed to his warnings and told him that they were the ones that should choose what's best to protect themselves. Medivh then said that he will find another who will heed his warning and that, now, their fate is their own.
Transcript from the mission
Unknown ambassador: "We've received reports that the orcs are regrouping."
Unknown ambassador: "Certainly the recent attacks against the internment camps are evidence enough."
Unknown ambassador: "Agreed ... the Horde is on the move!"
Unknown ambassador: "This is absurd. My nation will not standby and watch as the Horde masses on our very doorstep!"
Kirin Torambassador: "The orcs are not our primary concern here. How many times must I repeat myself? King Terenas, you must heed my warning. This plague that has gripped the northlands could have dire ramifications."
Unknown ambassador: "Plague? You wizards are just being paranoid!"
Unknown ambassador: "Let's keep all this in perspective. Even if this plague does pose a threat to us, what are you proposing that we do?"
Kirin Tor ambassador: "It is simple. As I have said, the Kirin Tor are already prepared to place the villages under 'strict' quarantine."
Terenas: "I will NOT institute quarantine without proof of your claims, ambassador. The people of Lordaeron have suffered enough without becoming prisoners in their own lands."
Medivh: "Yet prisoners they are, good King."
Terenas: "What is the meaning of this? Who are you?"
Medivh: "Humanity is in peril! The tides of darkness have come again, and the whole world is poised upon the brink of war."
Kirin Tor ambassador: "Enough of this! Guards, remove this madman!"
Medivh: "Hear me! The only hope for your people is to travel West, to the forgotten lands of Kalimdor!"
Kirin Tor ambassador: "Travel West?! Are you mad?"
Terenas: "Hold ambassador. I don't know who you are or what you believe, but this is not the time for rambling prophets! Our lands ARE beset by conflict, but it shall be WE who decide how best to protect our people, not YOU! Now begone!"
Medivh: "I failed humanity once before, and I will not do so again. If you can not take up this cup, I shall find another who will."
Medivh: "A warning has been given. Their fate is now their own."