Star Wars Used Vader's Order 66 Jedi Trick Before Revenge Of The Sith
Darth Vader's Jedi trap of Order 66 in Star Wars: Episode III - Revenge of the Sith was used at least once before in the High Republic era. There is a sense in which the entire Clone Wars were the perfect Jedi trap, designed to wear them down. As explained in Matt Stover's superb novelization of Star Wars: Episode III - Revenge of the Sith, they were irresistible bait, fought by expendable proxies, and they left the Jedi exhausted and weary. Order 66 was the culmination of this, with the Grand Army of the Republic turning upon their Jedi generals and gunning them down at Palpatine's command. As brilliant as it was, however, it was a strategy already used by Star Wars once before.
Palpatine's schemes were always layered, with numerous fallbacks and failsafes, and Order 66 was no different. The newly-christened Darth Vader led the clone troopers on the Jedi Temple, and once it had been taken he activated the Jedi recall. Designed to be used only in the direst situations, when the entire Jedi Order was judged to be at risk, this sent a signal across the galaxy calling all surviving Jedi back to Coruscant. It was a masterstroke, as any Jedi who survived Order 66 would naturally believe this was just the kind of situation when a recall would be issued. Thus, they would rush back to Coruscant, believing they were obeying the Council's wishes but instead exposing themselves to Darth Vader and his Imperial Inquisitors. Little wonder Obi-Wan Kenobi and Yoda knew they had to deactivate the Jedi recall, and were forced to infiltrate the temple.
It seems the Jedi recall seen during Order 66 was used at least once before, during the High Republic Era, some 200 years before Qui-Gon Jinn stumbled upon Anakin Skywalker on the planet Tatooine. This was a time when the Jedi and the Republic were at their height, but their bold advance into the Outer Rim exposed them to threats such as the Nihil. The Jedi based themselves at Starlight Beacon, a space station that helped Republic ships navigate the turbulent hyperspace paths of the Outer Rim. The Nihil launched a devastating attack on the space station in a story told in Claudia Gray's novel Fallen Star. This High Republic loss was the Jedi's greatest defeat before the Clone Wars, and it likely taught the Sith a great deal about how their adversaries would respond to a crisis. Daniel Jose Older's novel Midnight Horizon continues the story, revealing the Jedi activated the recall in the aftermath of Starlight Beacon's destruction.
It's easy to see why the Jedi triggered the recall during the High Republic Era. The destruction of Starlight Beacon was a crippling blow to the Order's morale, and some of their most celebrated Jedi Masters died during the Nihil attacks. Worse still, the Nihil had also found a way to turn the Force itself into the Jedi's greatest weakness, because they had acquired Force predators known as Levelers that disrupted the Force and then preyed upon Force-sensitives. Suddenly vulnerable, the Jedi withdrew from the galaxy and assembled at Coruscant, presumably planning a counterstrike while they licked their wounds. They abandoned Jedi temples across the galaxy, and ultimately would never return to them.
The Sith will have watched the Jedi's war with the Nihil closely. After all, this allowed them to understand exactly how the Jedi would respond to a time of crisis, and that very predictability could be used as a potent weapon against them. Thus Palpatine's plans incorporated the recall beacon, and Darth Vader, recognized by the temple's security systems as Anakin Skywalker, was the perfect one to trigger them in Star Wars: Episode III - Revenge of the Sith.