The execution of Star Wars' Order 66 in Revenge of the Sith marked the downfall of the Jedi Order and the Galactic Republic, but the unseen victims of the initiative were the Wookiees of Kashyyyk. The Wookiees, originally wishing to stay neutral in the Clone Wars, joined forces with the Republic to fight off a Separatist invasion, a mistake that would later prove tragic. After facing insurmountable odds and bravely defending their homeworld from the droid army, the Wookiees were betrayed by the clones sent to aid them and found themselves slaves to the Imperial war machine for decades to come.
During the Clone Wars, the planet of Kashyyyk represented a strategically important asset to the Republic, being rich in oil refineries and located along a series of hyperspace lanes critical to military transportation. As Mace Windu explained, it was a system the Republic could not afford to lose, so when the CIS launched a major offensive to claim the planet, the Jedi wasted no time in deploying the 41st Elite Corp of clones under command of Masters Yoda, Quinlan Vos, and Luminara Unduli to aid the Wookiees. Although the technologically advanced Wookiees were highly skilled warriors, they were in desperate need of the Republic reinforcements due to the sheer volume of battle droids attempting to claim their capital city of Kachirho. While successful in thwarting the CIS invasion, the victory was short-lived as Palpatine would enact Order 66, changing the fate of the Jedi and the planet Kashyyyk forever.
When Commander Gree received his orders to assassinate Master Yoda, the Republic was already solidifying its victory in the battle. However, when Yoda sensed the impending danger and killed the commander, Chieftain Tarfful and Chewbacca took responsibility for evacuating the Jedi Master from the city before they could be captured. In the now-non-canon Legends, this effort led to a small Wookiee uprising in which their efforts to aid Yoda in his escape led to a violent chase by clone troopers and high Wookiee casualties. Although the escape was successful, the clones would not forget the actions of the Wookiees, and immediately began a brutal occupation of their world that lasted to the end of the Galactic Civil War, making them also casualties of Order 66.
Upon establishment of the Galactic Empire, Kashyyyk was doomed to a future of suffering and servitude. The empire legalized slavery of certain species, including the Wookiees, and upon enslaving much of the population of Kashyyyk, put the natives to work. Their physical strength and technological savvy made them ideal labor for the empire, and they were forced to tear down their sacred Wroshyr trees for lumber, and harvest crops meant to feed the Imperial war machine. Those not kept on the planet were shipped off-world, some even sent to construct the Death Star. Thousands of other Wookiees would meet their deaths merely months after being sent to the spice mines of planet Kessel, depicted in both Solo: A Star Wars Story and Star Wars Rebels.
Although the Wookiees would attempt a number of uprisings against the imperial occupation, including battles with the help of Saw Gerrera and Cal Kestis, the Empire was able to quell many of their insurrections. Their actions during the end of the Clone Wars to defend the Jedi were not forgotten when the Empire was formed, and after continued rebellion over multiple decades, the Empire even chose to make an example of the planet and massacre countless Wookiees as a show of power. The Wookies would not be free of the oppression until the fall of the Empire after the Battle of Endor, but with their casualties far outnumbering those of the Jedi Purge in Star Wars, the Wookiees were in many ways the unseen victims of Order 66.
