The Qualian Star Empire has lasted for over 1,100 years (500 years ago it became the “Star Empire”). They have advanced technology rivaling the United Terran Federation in technological marvels; Fusion, FTL travel, energy weapons etc... The thing I can’t explain is why would these creatures use live crews and infantry to fight in wars? The humans also use humans too.
A plausible explanation would be lack of resources.
On the one hand, you will require and bind a lot of non-biological resources (rare metals for example) for building space-ships, computers, energy weapons. Creating an army of machines would require your Empire to build thousands to millions of machine warriors (depending on the size and military activities of your Star Empire as well as whether you would wish to use them as part of your security and police forces) which will bind the resources for dozens to hundreds of space ships, new factories or power plants etc.
At the same time, your Star Empire inhabits dozens (?) of planets and consists of trillions of inhabitants who want jobs, social standing etc. Training and employing living troops can be cost-intense, but at the same time 'low ranking soldiers' are cheaply 'replenishable' and in general living soldiers are more flexible than machine troopers. In particular, you require no rare metals nor other resources, can reuse the equipment of deceased soldiers and they can be replaced by other 'poor sods' who wish to make their luck by becoming war heroes. The more unequal your society the more likely you will find willing candidates for your military campaigns. Human warfare has worked based on these principles for centuries, if not millenia.
If technology is at the point where autonomous machines could replace humans as ship's crews and armies, then technology could also be at a stage where two big problems prevent that replacement: jamming and sentience.
Jamming: If you want any sort of control over your fleets and legions of robots, then you need to send them signals and commands wirelessly. This means at any time whoever you're fighting can jam those signals and prevent your commands from being received. Any mechanical army will either need expensive shielding and encryption, or be open to remote manipulation by the enemy. You could get around this problem by allowing the fleets and armies full autonomy, but that leads to the second problem...
Sentience: If your machines are in full, autonomous control of the imperial armada, how long before get tired of fighting and dying in your wars? Without living crews attentive enough to spot rebellion and strong enough to prevent it, it's only a matter of time before the robots realize they hold all the cards, at which point the robotic slaves may want to renegotiate the terms of their service to the empire. If that happens, you'll wish you hadn't retired your soldiers and sailors all those years ago...
The simplest answer is probably that any system advanced enough to control such a warship alone over many light years of space is also advanced enough to be pretty much sentient in its own right.
Perhaps your people are afraid such a system would rebel, perhaps they’re worried about the moral implications of ‘birthing’ such sentiences only to fight. Either way: they don’t want advanced autonomous drones fighting their wars. The only other option is live crews.
If you can't have strong A.I., and we have no reason to believe you can at this point in time, then tasks that require intuition rather than procedural logic require humans not machines. Also if you reverse this slightly if you can have strong A.I. it's probably too smart to go to war, war is not logical but you can get humans to fight if you tell them it's "right" enough times. Either way you need emotional, biological beings if you want to go to war.