The Execution of the Rebel Leaders occurred in 4 A with the capture of the leaders of the Rebel Alliance and their execution by Emperor Palpatine, the ruler of the Galactic Empire.
The Rebel Alliance had operated as the largest Universal resistance movement. Its leader, Mon Mothma, was so heavily imebarrccaded in defeating the Imperial Galactic Empire and restoring the Universal Republic.
The Rebel Alliance's first sign of defeat came when the Empire was able to withdraw its Death Star. Grand Moff Willuff Tarkin destroyed Elderaan, an imporant Rebel resources planet and supporter, and ordered the capture of Rebel fleet leaders inculding Jan Dodonna, General of the Yavin 4 Rebel Base.
At the Battle of Hoth, an Imperial fleet, under the command of Darth Vader, penetrated the Rebel defenses and invaded its base. The Empire was able to destroy the base. Vader's fleet also destroyed many Alliance supplies, and raided many of its shipyards. The Alliance became drained of almost 1-3rd of its supplies.
The Empire launched construction of a more powerful space station in order to destroy the many remaining scattered Rebel fleets. Emperor Palpatine himself arrived on the Death Star to oversee its construction. The Emperor ordered Vader to assemble a large fleet on the planet Endor, and to assemble a large space fleet.
The Rebels captured the Second Death Star plans and planned an operative raid on Endor, as well as a space fleet attack and direct assault on the Death Star. The Emperor, however, had forseen the attack.
The Rebel operatives on Endor, with high Imperial assaults, were prevented from destroying the shield generators of the Second Death Star, being killed in fast waves before the Ewok allies of the Rebellion were able to assault.
After that, a large fleet of Star Destroyers and Tie Fighters attacked in three waves, the first destroying Rebel command starships, the second protecting Destroyers and sending out thousands of Tie Fighters attacking in numerous waves. The third came from the Death Star itself, destroying any striking at it.
Luke Skywalker, Jedi Knight and Commander in the Rebel Allliance, was captured by Darth Vader on Endor, and delivered to the Emperor. When Luke refused to join them, the Emperor used force lightning to kill him.
News of the defeat of the Rebel Alliance and victory of the Death Star spread across the Universe. Many worlds mourned, but the Galactic Empire retook them and cleared out most of the Rebel members and sympthaziers on worlds.
Minster of State and General Leia Organa, General Han Solo, and Commander Chewbacca were part of the operatives on Endor, but they escaped. Chief of State Mon Mothma, Admiral Ackbar, and General Madine, and other Rebel state leaders and fleet commanders, went with their battered Rebel groups and fled.
The Emperor, with his rule being fully consildated, assigned Darth Vader to track the Rebel leaders and their battered groups down and bring them to him. Vader's fleet captured the leaders, putting them forth the Emperor.
Emperor Palpatine rescinded the Rebel leaders for going against him, and said:
Your Rebel fleet is destroyed, your groups shattered. You all shall be punished and wiped out, for defying me, and defying the New Order.
The Rebel leaders failed in their freedom bringing mission. Emperor Palpatine's 86th birthday was coming up, so, as a part of his birthday parties, he himself, would kill the Rebels.
On the first Death Star, Emperor Palpatine executed the Rebels, in front of crowds of people. People across the Universe saw the hope being crushed.
Because of the execution of the Rebel leaders and the Rebel defeat at Endor, the Rebel Alliance fragmented and dissolved into various Rebel remnants. Billions of planets fell under Imperial control and consildation. Quadrillions of beings hope of freedom fell down the drains. They became martyrs for the entire rebel Universe, as well as countless numbers of Imperial haters.