"It would depend on the circumstances. If the demographics are right, having 10-15% of a population die of old age in a 10-15 year period wouldn't be unusual. What do you think government would do about this, and why don't you answer the original question?"
These people didn't die of old age. They did from famine and disease following the collapse of the central government. So, do you think the prevention of the deaths of a million people from disease and famine is a legitimate function of government?
The original question? By that I presume you mean do I think any central government could have prevented this? Well, it happened after the central government collapsed, not before.
Post hoc ergo propter hoc. I bet you didn't know it, but I put a voodoo curse on them, shortly before the government fell and all those people died. So now you know the real cause of all that suffering...
But can you prove that "after this" really means "because of this"? Are you sure that the government itself didn't create the circumstances that led to starvation? In other words, maybe the starvation came because the government didn't fall soon enough.
The prevention of famine and disease can be a legitimate function of government, but there is no reason the it can only be done by government, or that it must be a central government.
The original question? By that I presume you mean do I think any central government could have prevented this? Well, it happened after the central government collapsed, not before.
Then you are drawing conclusions based on flawed logic, easily demonstrated by the simple obseravation that there are many cases of millions of deaths having been caused by disease and famine created by a central government.