Yep. They sent a task force of three behemoths (which are like flying fortresses, in that they were fortresses that freaking flew) to kill three great dragons, because they didn't like that the dragons were teaching people how to build shelters against the Horrors; the Therans had a monopoly on that magic among metahumans, and wanted to everyone to pay them in cash and slaves for the right to survive. The Therans had the most powerful metahuman mages in the world at a time that the manacycle was at its peak, an army that was 10% adepts, and banks of magitek fire cannons. They ambushed and killed two of their targets still in their lairs, but lost one behemoth in the process. The third target--we know him now as Ghostwalker--was gone when they got there, along with all his stuff.
Soon afterwards, three dozen prominent Theran citizens who had agitated for or profited from the strike on the dragons are found mysteriously dead. Ghostwalker was seen perched casually on a statue just outside the Theran capital, just to make sure they knew who did it. Dragons don't fight fair.
The third great dragon to be killed by the Therans was Vasdenjas, who took the hit on purpose to protect the airship Earthdawn during the battle of Skypoint. The alliance of local kingdoms and dragons still destroyed Skypoint, a naval base in the form of a city-sized platform intended for the aforementioned behemoths to land on, and drove the Therans out of the region.
You can kill a great dragon, but it isn't easy or cheap... and God help you if you miss the first shot, because you won't get a second one.