We've covered the War of Ancients in our previous Dragonflight posts: for the sake of this post we'll do a really fast recap. There was a really big magical well (the Well of Eternity) at the heart of the ancient continent of Kalimdor, which made up all of Azeroth's landmass at the time. Night elf ancestors found the well, tapped into its power, and built a massive civilization using it. Some night elves thought maybe this was a mistake, but most adored their leader, Azshara, and didn't see a problem. Then Azshara and her closest advisors the Highborne thought it would be a great idea to let Sargeras, the lord of the Burning Legion, into Azeroth to kill most everybody. Sane night elves, the various dragons, a few guys who traveled in time (this is important later, because it was Nozdormu who sent them back in the first place) and other powerful spirits of the world banded together to stop this because the idea of being a snack for a crazy titan and his legion of maniacs didn't appeal to them.
Then one of their own, the Aspect of Earth Neltharion (to be known thereafter as Deathwing), betrayed them all with the help of a magic artifact called the Dragon Soul that he'd tricked the other four aspects into donating power to, wiped out most of the blue dragons, and effectively ended the power of the Dragonflights to directly interfere in Azerothian history. It was up to the mortal races of Azeroth to steal the Dragon Soul from Neltharion, wherein it was used first against, and then to aid Sargeras' portal into Azeroth. Eventually the Well of Eternity itself was destroyed to prevent Sargeras from entering the world but a new one was created on the slopes of Mount Hyjal. Meanwhile, the black dragons, servants of Deathwing went to war with the other dragons, doing massive damage to the few remaining blues but having a harder fight against the greens, reds and bronzes.
Nozdormu was one of the three aspects who imparted his blessing to the first World Tree, Nordrassil, since it was his power over time that allowed the ancient night elves to regain the immortal agelessness (night elves can die, they just don't usually die of old age, you have to kill them) they'd lost when the Well of Eternity was destroyed. Since Nordrassil was set to cover the second Well of Eternity it's possible Nozdormu simply tapped the Well for the power.
At this point Nozdormu more or less takes himself out of the equation: you very rarely see the Aspect of Time himself interfere with current events. His dragonflight, on the other hand, settled into their work protecting time from meddlers and keeping events in their proper order. It's hard to say with a group that is constantly mucking about with history and timelines how long they've been about it, really. For those of us who aren't time traveling dragons, there were about 9000 years between the events of the War of Ancients and the first Silithid incursion under the Qiraji, which is where the Bronzes step up and take charge of a major war. As a result of Nozdormu's tendency to stay offstage, his prime consort Soridormi, son Anachronos, and other pivotal figures of the Bronze Dragonflight have as much or more impact on the world as the Aspect himself does, as it is they who end up making most decisions.
Bronze dragons were not particularly likely to get involved in a temporally linear war like the one known as the War of the Shifting Sands, even with the threat of an old god hanging over their heads had it not been for the direct aggression of the Silithid armies under Qiraji leadership. Indeed, the Bronzes refused to aid Fandral Staghelm, leader of the night elven forces defending Kalimdor from the Silithid and their Qiraji masters when he asked. After defeating Fandral Staghelm by killing his son Valstann in front of him, the Qiraji pushed the elves out of Silithus entirely, made their way through Un'goro (where they were stymied by the Titan's handiwork, the pylons that preserved the region) and went so far as to attack the Caverns of Time.
Incensed, Anachronos joined the fray, and enlisted help from the red, green and blue dragonflights. With the aid of Merithra of the Dream, Caelestrasz and Arygos, the bronze dragons pushed the Qiraji back through the 'god lands' (the Qiraji name for Un'Goro Crater as written in the Prophecy of C'thun) and slowly, inexorably back into Silithus itself. The battle was no easy: dragons died to the exotic magical powers of the Qiraji forces Grakkarond, a powerful bronze dragon (and one named very similarly to Galakrond, progenitor of all five dragon aspects, so possibly a very old one as well) died in combat with Ossirian, a construct of the Qiraji Twin Emperors. Despite this, however, the dragons proved to be enough to tip the scales and the Qiraji were driven back to their temple city, Ahn'Qiraj, where thanks to the sacrifices of their allies the bronzes and their night elf allies managed to seal the enemy forces away. Anachronos created from a nearby scarab the massive gong that hung outside the gates and from the limb of a nearby fallen dragon, he shaped a scepter that could be used to strike the gong and unseal the trapped Qiraji when sufficient forces finally existed to wipe them out once and for all.
It was here that Anachronos again showed how little he understood the minds of mortals. First he refused to help Fandral, an act that indirectly cost the night elf druid his son, and now instead of destroying the Qiraji he not only settled for a policy of containment, he handed the device necessary to release said containment into the hands of the elf he had already bred resentment into. Not surprisingly, Fandral rejected this gesture, smashing the Sceptre of the Shifting Shands into the sealed gates of Ahn'Qiraj. Offended, Nozdormu's son gathered the fragments and entrusted them to the various dragonflights who had lost potent offspring in the war. He kept one, and vouchsafed one to Azuregos, Eranikus and Vaelestrasz. (This ended up being pretty bad news for Eranikus and Vaelestrasz. Azuregos was smart and gave his to a giant fish.) Interestingly enough for a dragon so involved in time, Anachronos does not seem to have seen the eventual fate of the chosen shard guardians coming.
A thousand years would pass before the Bronze would again become so involved with mortals.