In 19 BBY, in the closing days of the Clone Wars, Darth Sidious, publicly Supreme Chancellor Sheev Palpatine of the Republic, initiated secret protocol Order 66. Under this directive, the Republic's clone troopers, compelled by behavioral modification chips implanted in their brains, turned on their Jedi generals in a galaxy-wide purge. With the majority of the Jedi Order annihilated and its few survivors scattered in exile, Sidious proclaimed himself as Galactic Emperor before the Senate and formed the Galactic Empire, and the clones became the first generation of Imperial stormtroopers. In the days following the Empire's birth, Palpatine dispatched Governor Wilhuff Tarkin to Kamino to discuss the future of the clone program. With the end of the Clone Wars, the Sith Lord believed that the clones had largely fulfilled their purpose, and that the continued cloning of soldiers was too expensive to maintain. Tarkin likewise shared the Emperor's views, and believed that a conscription-based army could carry out the clones' duties at half the cost. Working in conjunction with Vice Admiral Edmon Rampart, Tarkin initiated Project War-Mantle and sanctioned the creation of an experimental unit of non-clone Elite Squad Troopers placed under the command of clone commando and sharpshooter Crosshair. The squad's success during their early missions impressed Tarkin, who left the project in Rampart's hands to continue.
Over the next several months, Rampart embezzled funds meant for cloning operations on Kamino and instead directed them towards Project War-Mantle. Clandestinely, a training facility was set on the Outer-Rim world of Daro, where non-clone stormtroopers were trained by clone commandos. Rampart at various points attempted to propose the Imperial Defense Recruitment Bill to the Imperial Senate, which would allow the Imperial Military to legally begin the mobilization of non-clone soldiers, but the bill was tabled several times. Ultimately, the Empire's cloning contract with Kamino was terminated, and after extracting valuable cloning equipment and essential personnel, Rampart was ordered by Tarkin to bombardment Tipoca City with his fleet of Venator-class Star Destroyers.
After several more months, Rampart again proposed the Defense Recruitment Bill to the Senate, and found the support of many more senators this time around, as many believed the Empire was vulnerable after the destruction of Kamino's cloning facilities, which was covered up as being the result of an apocalyptic storm. Rampart also proposed that aging clones begin to be phased out of the Imperial Military as recruited soldiers would begin to take up the mantle, which a handful of senators rejected to, chiefly Pantoran senator Riyo Chuchi. Despite several conversations with Rampart to drop or at least modify the bill to compensate the clones once retired, Rampart dispatched an assassin known as Clone X to eliminate Chuchi. Rampart had earlier deployed the assassin to kill two clone officers that had served aboard his Venator during the bombardment of Kamino, Slip and Cade, as the two threatened to expose his lies to the senate. Chuchi was ultimately saved by from her assassination by rogue clone Captain Rex, who had come to Coruscant to extract Slip before his death. Working in the best interest of his clone brothers, Rex begun to work with Chuchi in order to stop the passing of the Defense Recruitment Bill, and called upon the rogue commandos of Clone Force 99 to assist him.
Sneaking into the Coruscant shipyard, Rex and the Bad Batch intended to steal the command log from Rampart's personal Venator, which was docked and undergoing repairs. The command log contained a recording of Rampart's fleet destroying Tipoca City, which Chuchi wished to use to incriminate Rampart before the Senate and have his bill tabled for good. The rogue clones stealthily entered Rampart's Venator and stunned the skeleton crew of clone stormtroopers left aboard as security. In order to access the command log, commando "Tech" was forced to activate the Venator. As starfighters, gunships, and clone stormtroopers swarmed the Venator, the command log was eventually obtained, and Rex and the Bad Batch exited through one of the ships escape pods.
By morning, the command log was rushed to the Imperial Senate and handed over to Chuchi by "Omega". As the command log was played and the Senate witnessed Rampart's destruction of Kamino, Emperor Palpatine appeared to address the Senate. Manipulating the situation to his favor, Palpatine declared Rampart a rogue element as he was arrested by clone shock troopers, but disingenuously expressed his shock of Kamino's fate. Seeding a sentiment of doubt regarding clones, Palpatine condemned the clones for "blindly following orders" and taking part in Kamino's destruction. Believing the galaxy to be best protected by a new army, Palpatine announced the age of the Imperial stormtrooper to the Senate, the first time the infamous term was used publicly. With this speech, the Imperial Defense Recruitment was passed, and the fate of the clones sealed.
In the aftermath of the chaos in the Senate, Rex and the Bad Batch reflected how Palpatine had still managed to sway to situation to his favor. Believing his skills were now needed more than ever, rogue clone "Echo" departed with the Bad Batch to join Rex's resistance, as the clones now faced an uncertain future. Senator Chuchi further pledged to continue fighting for clone rights in the Senate for as long as she could.
The effects of the bill could be seen almost immediately after its passing. Though clones were still allowed to serve in the Imperial Military, some units faced forced decommissioning for unknown reasons. Before departing for a mission some time after the passing of the bill, CT-9904 "Crosshair" witnessed three clone officers being forcefully retired and escorted out of the Imperial Inspectorate HQ. Elsewhere across the galaxy, "problematic" clones were being purged from Imperial ranks, with many ending up at the Tantiss Base on Mount Tantiss, to be experimented on by Doctor Royce Hemlock and his Imperial Advanced Science Division. Hemlock further insisted during the summit on Eriadu that all decommissioned clones be given to him to take part in experiments.