Timeline

A Timeline of Events With a Focus on Gnome Involvement

Year	Events
Unknown date	The titan-forged are created by the titans to fight the Old Gods. The titanic watcher Mimiron creates the mechagnomes within Ulduar in Northrend as servants and caretakers. Some mechagnomes leave to become caretakers at Uldaman in the Khaz Mountains.
< Year -3000	Mechagnomes are slowly turned mortal via the "Curse of Flesh" unleashed by the Old God Yogg-Saron. The mechagnomes of Northrend are unaffected, but those of Uldaman are turned into what we now know as gnomes. They escape the facility into the surrounding mountains.
< Year -2600	Focused on other matters, possibly technical advancement, gnomes completely neglect to document their past leading to a quick forgetting of where they came from over just a few generations. In what is now known as Dun Morogh, the gnomes etched a sequence of strongly secured habitats within the mountains.
~ Year -2600	Gnomes obviously play some part in global society with several gnomes sitting on the Council of Tirisfal, the secret council responsible for choosing the Guardian of Tirisfal.
~ Year -400	King Mechagon, the last king of the gnomes, led his followers in search of a mystical land of technology. It is unknown precisely what percentage of gnomekind followed him and how many stayed behind. This gnome kingdom would probably have been located somewhere in Khaz Modan, in its caves and hills. It is clear that by this point gnome technology was already quite advanced.
Year -170	The first properly recorded interaction between the dwarves and the gnomes of Khaz Modan. The dwarves were enamored by the gnomes technical abilities and struck up an alliance with them. They help build the foundations of Gnomeregan. The gnomes previously lived in the caves and hills of Khaz Modan, probably in Dun Morogh. It is unlikely that these two races had not met before this time as they had both played a part in global events for thousands of years, so its more likely that this just points to the start of their collaboration.
Year ~ -160	Assuming Gearshaft University was based in Gnomeregan and that it would have taken a few years to get construction going far enough to build such speciality buildings, we can place the founding of the university where both Sicco Thermoplugg and Gelbin Mekkatorque graduated from around here.
Year 0-4	The First War breaks out, the gnomes play a minor part in these conflicts.
Year 4-6	The gnomes aid their dwarven allies in the Second War, primarily supplying technologically advanced weapons and vehicles like Flying Machines, Submarines and explosives. Judging by the modern submarine models, its likely that the submarines in the Second War were completely operated by gnomes.
Year 6	The Horde lays siege to Gnomeregan during their invasion of Lordaeron. The Alliance intervened and won a decisive victory.
Year 6-18	The gnomish electorate choose Gelbin Mekkatorque to lead their people as High Tinker for the first time due to his many exploits. Apparently he was quite young at this point.
Year ~10	The Deeprun Tram is built between Ironforge and Stormwind. It was the priced design of High Tinkerer Mekkatorque.
Year 20-25	Gnomeregan gets irradiated by Sicco Thermoplugg and invaded by troggs. The gnomes are unable to participate in the Third War. Shortly after this the gnomes moved to Ironforge and built Tinker Town there.
Year 27	Excursions to Northrend reveal stunning facts about gnome and dwarven history. Their mechanized past and the "Curse of Flesh" is revealed to the world and to the gnomes.
Year 28	New Tinkertown is founded after a first assault is made on the capital of Gnomeregan.
Year 33-35	The mysterious island of Mechagon is found and "newly" mechanized gnomes who had either never seen gnomish society or been away from it for many centuries found their way to the Eastern Kingdoms and the Alliance.