It's how empires fail. 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 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)?
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."
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.