Army pensions were part of it, but it was the expansive empire and the cost to maintain it (through armies) that caused a lot of the problem. And how did they pay their armies? By debasing the currency.

Empire building works as long as the countries conquered produced more wealth than it took to conquer and maintain the new lands. Today we do not conquer as much with armies. Today financial warfare is waged and the armies are more used to maintain strategic partners for the financial warfare. But empire building still goes on today. Just in a somewhat more humane form. Somewhat.

When Rome finally fell, the armies sacking it were welcomed because the residents thought the new rulers would be less oppressive than the current.

In your reading, know what one of the first things done by the new ruler? Insist and implement sound money policies.

None of this is new. It happens over, and over, and over, and over in historical evidence. The only thing that is new is the current generations have not learned from history so are destined to repeat it. Maybe one other thing is new. The entire world being on fiat currency, all debasing at the same time, with a simultaneous world wide currency failure. That would be new.

John