The Blockade of Kashyyyk was a blockade established by the Galactic Empire over the Wookie homeworld of Kashyyyk in 1 ABY, during the Galactic Civil War.
Following the destruction of the First Death Star, Palpatine ordered Darth Vader to hunt down the Rebels responsible for the space station's destruction. But as the rebels had evacuated their base on Yavin, the Empire had no idea as to where the exact location could be. A number of planets were suspected to hide the Rebel base, including Kashyyyk, which was known for having rebel sympathies due to it's population's enslavement by the Empire.
As Han Solo and Chewbacca were leaving Tatooine on one of their typical flights, they were intercepted by two Star Destroyers of the Empire, who had recognized the Falcon from a previous encounter during the escape from the first Death Star. After an attack by the two Star Destroyers, Solo sent the Millennium Falcon into lightspeed. However, the Empire traced the course that the ship had set, and tracked their route to Kashyyyk. Now having sufficient information, Vader ordered a full blockade of Kashyyk.
Darth Vader sent 25 ships of his elite Death Squadron, led by his personal flagship, the Executor, cutting off all contact and trade to and from the planet, while Imperial troops searched for the Rebels of the surface. Upon arriving near the atmosphere of Kashyyyk, the Falcon found itself under fire from TIE fighters, who were guarding the planet. Down on Kashyyyk, Imperial Agents entered the home of Chewbacca, where the family was preparing for Life Day.
After doing an extensive search of the home, the Imperial Agents couldn't find a trace of the Rebels. Lumpwarrump Chewbacca's son, had gotten ahead of the Imperials; he created a device that tricked the officers into leaving, leading them to believe that the Rebels had already left Rwookrrorro, thus sending the Imperials on a wild goose chase to a across the planet. Han and Chewbacca arrived at the home, and later, they all celebrated the holiday.
By the time the Imperials had returned to Rwookrrorro, after realizing they had been deceived, the Rebels had long gone. After completely combing the planet, with little evidence there had ever been a rebel base on the planet, Lord Vader called the blockade off.
In response to the defeat, Palpatine decided to start over, by ordering the immediate resuming of the construction of the Second Death Star over Geonosis. Because of the humilitaing defeat, he punished the Wookiee population of Kashyyyk with signing an order enslaving 10,000 more Wookiees in order to complete it. Ironically, though, the family of Chewbacca was able to escape this fate.
The blockade would lower the morale of the Imperials stationed on the planet and the Wookiees, which had been fed lies by the Empire concerning the treatment of Wookiee slaves, or "indentured laborers", and led many to join the several Rebel sects scattered across the planet (which had avoided detection during the time of the blockade), which, in turn, would indirectly help the New Republic (successors of the Alliance) to achieve victory during the Second Battle of Kashyyk.