Archimonde, being the bonehead that he is (was), walked away without finishing the job. The Kirin Tor sealed the remains of the city within a supposedly impenetrable shield so they could rebuild yet again, this time rebuilding far more than just their city. In the Scourge and Archimonde's assault, the nation lost more than it ever has before, including some of its ruling council and the de facto leader Archmage Antonidas.
Very recently, Dalaran has emerged from its shell and rejoined the world to thwart the Blue Dragonflight, led by the aspect Malygos who believes mortals are not meant to wield magic at all. To some extent, the Kirin Tor agrees with the Blue Dragonflight; magic shouldn't be thrown around as haphazardly as it is... but they don't really agree with taking it away complete, for obvious reasons.
Not only has the Kirin Tor stepped up to stop Malygos, they've taken the fight to him in the most literal sense possible. They've used their magic to dig Dalaran right up out of the ground, sewers and all, and float it up to Northrend. At the behest of the new Archmage of Dalaran, Rhonin, the Horde has been allowed into the city en masse for the first time. Well, the first time they've been invited in, anyway. History has shown they sort of have a tendency to trample on through whenever they want.
While many see it is a necessary step, others such as Rhonin's own wife still haven't forgiven the Orcs or the crowd they roll with such as the Forsaken and Blood Elves. The Kirin Tor have managed to spark a cold (gang) war of sorts within their own city because of this. The High Elves of the Silver Covenant lay claim to half of Dalaran and the Blood Elves of the Sunreavers claim the other half, in the names of the Alliance and the Horde respectively.
That's... pretty much the history of the city itself. To sum up: Small city of Mages founded by Humans, completely overrun multiple times, rebuilt multiple times. It now floats over Northrend as a base camp for the Nexus War and a sanctuary for those fighting against the Scourge.
While those were the major historical events for the nation, most parts of modern civilization have some ties to the city, whether it be something such as Jaina Proudmoore having trained under Archmage Antonidas, or something as simple as rulers and major figures having passed through the city. While the coins you can fish up in Dalaran are meant to be funny, they really drive the point home about how many stories have had crossroads in Dalaran. Arugal, Kel'thuzad, and Kael'thas have all had their 'beginnings' in Dalaran, and many, many more have passed through on their journeys.
Even if Dalaran doesn't have the best record when it comes to war, the city certainly has a special place in the hearts of Humanity, and probably even Elf-kind these days. Plus it's super pretty.