The soldiers within the Clone Army of the Republic were created for the sole purpose of serving, fighting, and dying for a government they not only were indoctrinated from birth to be loyal to, but also genetically modified to be compliant to its authority and command structure. They were viewed as mere money making cattle from their creators, and later as dispensable assets from their Republic masters who treated them as if they were droids. But before they were even forced to fight a war they barely understood, the creation of the clones was quite cruel in of itself.
When the Kaminoans first gained their purchase order for the army, they had to undergo many trial and errors before they could successfully create soldiers in a timely manner and later mass produce them in the millions. These initial trial and errors resulted in many of the first clones to be born with physical and mental defects, all of whom had to undergo tests for the scientists to discover solutions to their disabilities before eventually being terminated once their usefulness to science was fulfilled. The first real batch of clones to be grown into able bodied men were also slated for termination by the perfectionist Kaminoans as they viewed them to be too independent, but their destruction was stopped by one of the Mandalorian instructors employed for training, who later formed them into the Null-class Advanced Recon Commandos.
The same Mandalorian later adopted them all as if they were his sons. Eventually the Kaminoans created the final modified genetic template that would serve as the basis of the majority of the clones that would fight in the clone wars. This template not only increased the clone’s physical traits, such as increased lung capacity and muscle endurance, but it also tempered with them mentally.
The clones were modified to be docile to authority figures and were made dependent to command structures. The most significant modification to the clones was their accelerated aging process, which made them age twice as fast a regular Humans. Although this allowed the Kaminoans to reach their order for a grand army in a timely manner, it did result in severe side effects that would plague the clones for their entire lives.
Not only did the accelerated aging process essentially cut the clones’ lives in half, it also brought up severe deterioration in them both mentally and physically once they began to reach their later years, making many of them unfit for military service once they reached the age of 20, or in clone years, the age of 40. As around that age many of them experienced a sharp decline in their mental and physical health. They were unable to think as sharply or move as swiftly as regular humans who were physically the same age.
In some cases, a clone’s mind deteriorated so much that they went mad; which was only amplified more once they began to experience PTSD after they were decommissioned from the battlefield. The childhood of clones was as strict and orderly as one might expect it to be. They were treated by their Kaminoan creators as mere cattle, who were willing to terminate them for the smallest of defects.
Though said terminations were discontinued once the Jedi took over the cloning facilities. The first years of a clone’s life consisted of countless hours of combat training, battlefield simulation practices, and essentially brainwashing as the clones were made to digest Republic propaganda to ensure their absolute loyalty once they became active soldiers. Although originally clones who showed high signs of independent thought were killed by the Kaminoans as they feared they would rebel, this procedure was later overturned by Jango Fett and the other hired Mandalorian instructors as they began to train these independent thinking clones for special forces and high command positions.
Once the first units of clones were completed, they were thrown into battle almost immediately as they were dispatched to Geonosis and were given command to Jedi who had virtually no experience of leading armies. Due to this inexperience and such sudden accusation of an army, thousands of clones died on Geonosis due to poor decisions and lack of pre planning from the overconfident Jedi as they staged their attack. And the battles that they clones were forced to fight in were nothing like the simulations that they practiced in.
Sure the simulations prepared them to physically fight and survive in battle, but it did not prepare them for the true horrors of war as they witnessed their comrades, many of whom they literally grew up with from birth and considered to be their brothers, get blown into bits and obliterated on the battlefield right before their eyes. Although the clones were devastated by their losses, it did not weaken their loyalty or dedication for fighting for the Republic, which was a clear product of all the propaganda they consumed during their youth. Ironically, despite making the greatest sacrifices out of anyone in the Republic, the clones knew very little over what the war was really about.
Actually, some Arc Troopers with curious minds ended up spending their free time studying and following the politics of the Clone Wars to better understand what they were truly fighting for. Those who did usually learned enough to realize what they were fighting for was a sham and nothing like what the propaganda they underwent back on Kamino. These revelations resulted in some Clones to desert from the army.
And of course desertion was not allowed for clones, regardless of intent, as it was punishable by death. An entire unit of clones was created for the sole purpose of hunting down and eliminating clone deserters. Other clones who showed signs of possible disobedience were forced to undergo reprogramming.
Clones that died in battle and had their bodies retrieved by official Republic forces were treated no better than droids, as their bio matter and body parts were essentially recycled for reuse for the creation or treatment of other clones. They only received proper burials if their squadmates did so in secret in the middle of nowhere. Clones who were injured on the job were usually given cybernetics as repairs if they held a high or vital rank in the army; otherwise they were forced to retire if they were unable to fight.
The retirement of clones hasn’t been fully explored, but in Canon there was at least one retirement housing complex created for veterans of the clone wars on the planet Gorse. It was noted for being rundown and in very poor condition, implying that clone veterans were likely given the bare minimum for their service once they were retired. It’s safe to say that in Legends that clone veterans were treated similarly.
Under the Empire, some unfortunate clones were handpicked to be used in Imperial experiments that sought to create super soldiers and reverse the deterioration process that the clones were inevitably going to undergo from aging. One of these experiments was the dark trooper project, in which the earliest phase of these troopers saw clones being turned into cyborgs as they had their limbs forcibly removed and replaced with mechanical parts to enhance their combat abilities. In some cases, over 70% of their organics were replaced.
Many clones who underwent these experiments commited suicide after not being able to cope with the fact of being more machine than man. The dark trooper project was later abandoned after regular Human recruitment was introduced in the Empire for the Stormtrooper core. And just like with the dark trooper project, the clones themselves were abandoned over time as they were forced to retire and accept that they were going to be fully replaced by regular Human recruits, who they considered to be vastly inferior to themselves.