Origins and Romance
The only daughter and third child of Lord Admiral Daelin Proudmoore, the ruler of the island nation of Kul Tiras, Jaina grew up as a proud citizen of a prosperous member of the Alliance of Lordaeron. Hearing stories of the powerful Guardian Aegwynn as a child, Jaina was inspired to forsake the life of a princess at court to study as a mage at the great city of Dalaran. Although initially denied the opportunity, Jaina's hard work, skill and persistence would eventually pay off, and the Archmage Antonidas would grant her entry into the colleges of Dalaran, and eventually take her on as his apprentice. Some time before beginning her arcane studies, Jaina met Prince Arthas Menthil, Crown Prince of Lordaeron, and the two became quick friends, even sneaking out one night to look at an Alliance internment camp and its orcish prisoners. Her friendship with Arthas would eventually blossom into romance during her time in Dalaran, and the two became lovers, much to the frustration and jealousy of the high elven prince Kael'thas Sunstrider, who desired Jaina himself. Their relationship was a passionate one, but after a time, a combination of factors, including Jaina's studies as a mage, Arthas' growing responsibilities both as heir to the throne of Lordaeron and a Knight of the Silver Hand and the possibility of marriage, scuttled their love affair for a time. The two separated, and Jaina's focus remained to her training as a sorceress under Antonidas. Although young, her powers developed rapidly, and soon she had become a very powerful sorceress in her own right.
The Scourging of Lordaeron and the Exodus to Kalimdor
Even as Jaina rose to be an exceptionally powerful mage for her age, trouble began to stir in Lordaeron. The orcs, which had been defeated and enslaved following the end of the Second War, rose up once again, this time under the leadership of the benevolent and charismatic warrior-shaman Thrall. Under Thrall's guidance and through the embrace of the old ways of shamanism, a new Horde was formed, one that laid waste to the mighty fortress of Durnholde and had managed to evade all attempts by the Alliance to engage them. Meanwhile, plague gripped the northern villages of Lordaeron, all the while a strange prophetic figure who took the form of a raven spoke of doom threatening the entire world. Under a spell of invisibility, Jaina eavesdropped upon one such visit by the Prophet to Antonidas, the latter scorning the former's words and sending him away. Afterwards, Antonidas sent her on a mission to discover more about the plague, particularly to confirm the Kirin Tor's suspicions that it was magical in nature. To assist her in this task, Arthas and a company of soldiers joined her, the party travelling along the King's Road to see the afflicted villages firsthand.
What they discovered was beyond their wildest fears; the plague was indeed magical in nature, and it had the effect of killing the infected and reanimating them as the undead. Moreover, the plague was being spread by inflicted stores of grain, all marked in cases bearing the seal of Andorhal. Traveling to the town, they found that the grain had already been distributed and Andorhal itself was overrun by the living dead. The man responsible for this horror, an exiled archmage of the Kirin Tor-turned-necromancer named Kel'Thuzad, claimed he was acting in the name of Mal'Ganis, and was using the plague to fill the ranks of the undead army known as the Scourge. Hunting him through the hills, Arthas and Jaina slew Kel'Thuzad, but not before the necromancer taunted them for their folly, saying his death would mean little.
Traveling to the nearby town of Hearthglen, Arthas and Jaina were shocked to discover that the Scourge was bearing down on the community, thousands strong. As Arthas lead his troops and the local defenders against the undead, Jaina used her sorcery to summon Uther the Lightbringer and his knights, who arrived in time to save the beleaguered town. In the aftermath, Jaina was astonished by her former lover's frustrated and fanatical attitude towards fighting the undead, even as the mysterious Prophet arrived in an attempt to dissuade him. Arthas would hear none of it, however, and Jaina had no choice but to follow him to the city of Stratholme in hopes of defeating Mal'Ganis there.
When Arthas, Jaina, Uther and the Alliance troops arrived, they found that their worst fears had been realized; Stratholme had been infected with the plague. For the time being, the townspeople had not begun the transformation into the undead, but they could do so at any moment, prompting Arthas to launch a bloody purge of the city, massacring its unaware inhabitants before they could transform into more warriors for the Scourge. Horrified by this plan, Jaina and Uther tried to convince Arthas of some other alternative, but he scorned them, even disbanding the Order of the Silver Hand when Uther refused to follow his commands. Disgusted with her former lover, Jaina departed, refusing his demands that she aid him. Arthas would begin his bloody massacre of the people of Stratholme, then depart with his army to the frozen continent of Northrend to take the fight to the Scourge directly. Shortly after the purging of Stratholme, Jaina was visited by the mysterious Prophet, who gave her the same warning as before; set sail west towards the lands of Kalimdor, or risk the destruction of humanity and all of Azeroth. Unlike the others, Jaina heeded the Prophet's words, and organized a mass exodus from Lordaeron across the Great Sea, saving tens of thousands of people from the Scourge and eventually, the invasion of the Burning Legion itself.
War in Kalimdor