What is an example of an empire that failed liked this?

Sparta is the closest example i think of. all the men were soldiers and all the hard labor/farming were done by slaves/healots. eventually led to technological stagnation & societal collapse

Did Sparta actually fall because Thebes out innovated them on the battlefield? If so, perhaps an argument _for_ the military industrial complex as a nation’s savior. Perhaps you are thinking of classical Athens, and its loss to the Greek city-state of Syracuse in Sicily?

Arguably, Rome and the Praetorian Guard.

https://en.m.wikipedia.org/wiki/Praetorian_Guard

Rome fell because of the Praetorian Guard?

Not because of unsustainable conquest, a massive influx of slaves taking all the work, flawed institutional structures with only norm-based barriers to generals from seizing control of the government, and massive Germanic migrations due to reasons unknown (probably steppe people)?

The Praetorian Guard appointed Claudius as emperor, and had assassinated several others, all of which could be considered, arguably, a major step in the downfall of the Roman Empire.

Remember, this was a response to illustrate: ”When your military suppliers and contractors become large enough to buy the government, they grow like a malignancy, bleed the productivity and resources of the empire into building things that explode, and kill the host."

Not just Claudius, they were involved in a few imperial transitions.

But it's debatable if that's a military-industrial complex functioning in conditions of economic hazard. Like, advisors and royal courts plotting against the ruler is fairly common and historically never involved stock buyback schemes.

The more general phenomenon of what the parent is describing is rent-seeking becoming an outsized portion of society. When the rent-seeking class becomes too powerful they drain an unsustainable amount of productivity from the rest of society that eventually causes it to become weak/unstable and fall to internal or external forces. The Ottoman Empire is a good example of this.