Dalaran has been one of the most prominent nations in the Eastern Kingdoms since its founding, though it's actually quite small. A nation only thousands strong at its height has perhaps held more sway over world leaders in its time than any other nation, and has attracted the ire of some of the most powerful entities Azeroth has ever seen.
Dalaran, located in the heart of former Lordaeron territory, has been the center of Arcane knowledge since its creation, and could be considered the Humans' answer to Quel'Thalas, though the nation accepts Elves (and many others) in its ranks as well. Magic is Dalaran's lifeblood, and is even ruled through the strength and wisdom of its magi. Dalaran is a magocracy, a government ruled by a council of mages known as the Kirin Tor, elected by citizens of the nation. Their icon is the Violet Eye, with Violet being the motif used for the nation itself, and the color purple representing the Arcane as a whole in Warcraft (Arcane Missiles, Netherstorm).
Dalaran has been at war (or recovering from it) pretty consistently since the Second War, when Dalaran joined the Alliance of Lordaeron. The Second War being what it was and the Orcs being Orcs, Dalaran was quite nearly sacked but managed to hold on by a thread. The Magocracy quickly rebuilt, using an artifact they created and dubbed the Eye of Dalaran... and was immediately assaulted yet again. Teron Gorefiend, under orders from Ner'zhul (fulfilling a request from Deathwing), stormed the city yet again to steal the Eye.
While the Eye was later retrieved by Khadgar and the Alliance Expedition, its current whereabouts are unknown. It's extremely likely that it ended up back in the hands of the Kirin Tor, but it's never been specifically stated. Either way, Dalaran rebuilt. Again.
Then it was destroyed in the Third War. ...Again. This time its destruction came at the hands of Archimonde, summoned into Azeroth by the Scourge, who still feigned allegiance to the Legion at the time. Archimonde made it look really, really easy, too. He basically built a sandcastle that looked like Dalaran and kicked it over. Through the power of magic, the real thing crumbled, too. Ah, magic. We love you so.