From the Cambridge World History of Human Disease, , Section VII.7 "Disease Ecologies of Europe" by Stephen R. Ell (1993):
"[in the ancient world], the disease picture here suggests societies with significant overpopulation expanding into new territories and experiencing few major epidemics, until a point was reached when exposure to infectious epidemic disease began a process of demographic decline and cultural retraction."
For example, Hannibal invaded Italy commanding an army of around 40,000 mercenaries. These men had marched through Spain, across southern France, over the Alps and into northern Italy. At Cannae, it is suggested that Rome had 48,000 troops and 6,000 cavalry against Hannibal's 35,000 troops and 10,000 cavalry.
Compare that with the armies at the Battle of Pavia (1525), where Francis I was captured. It also involved a foreign army invading Italy over the Alpine passes. The battle involved 17,000 infantry and 6,500 cavalry (French army) and 19,000 infantry and 4,000 cavalry (Spanish - Imperial forces).
"Just as the greatest generals of the ancient world gave insights into disease demography, so also does the career of Napoleon Bonaparte, with which we may end this brief discussion of the eve of the Industrial Revolution. At the time of Napoleon, we again see armies in the field numbering in the hundreds of thousands of men."
What is the modern opinion of this population v. disease analysis ?
Hiya!
This theory might be extremely generously described as 'niche.' Frankly, it'd probably get you laughed out of the room at my home university. The problems with it are numerous and egregious. To name a few:
Accounts show that plagues and infectious disease outbreaks were absolutely common in the ancient world, and have been the bane of armies since time immemorial. This is not a new issue. From the Plague of Athens in 430 BC recorded by Thucydides, to accounts of crippling disease outbreaks among armies of Antiquity, or the plague of Justinian which devastated the Eastern Roman Empire, we have myriad accounts of disease being the long-time bedfellow of war.
The idea of comparing the numbers of troops at Cannae with those at Pavia to support this theory is, honestly, entirely meaningless. It's simply cherry-picking a large battle from antiquity (which, I might add, we have less-than-reliable figures for) and comparing it with a smaller battle from a more recent era, with no regard to the the context in which those battles were fought or the nature of war in their respective time-periods and regions, and then saying 'A is bigger than B, ergo this supports the above theory.' For instance, I could instead cherry-pick to say 'The 52 BC battle of Alesia involved more than 100,000 troops, but the 1812 Siege of Badajoz involved less than 30,000, ergo Napoleonic armies were smaller than Roman ones!' Or, to turn it around, 'the battle of Austerlitz was bigger than the battle of Zama.' It's entirely meaningless without context.
The size and composition of armies is always explained by the context in which they are created and raised. This theory ignores far more obvious, logical and widely accepted explanations for the varying sizes of armies over time and region, and instead attempts to draw tenuous links to epidemiological patterns. Disease has always been a critical factor of war, but to claim that armies were large in antiquity due primarily to the absence of disease is misleading at best and blatantly false at worst.
This "theory" seems to suggest there was some special point that "was reached when exposure to infectious epidemic disease began a process of demographic decline..."
This special point must have been after the plague in Athens during the Peloponnesian War.. Which wasn't just in Athens, but according to Thucydides:
It (the plague) first began, it is said, in the parts of Ethiopia above Egypt, and thence descended into Egypt and Libya and into most of the King's country. Suddenly falling upon Athens, it first attacked the population in Piraeus.
Possibly a quarter to a third of the population, including soldiers and commanders, died from this plague.
Of course that is just one example. But that is exactly what this theory seems to be doing. Picking a few examples and thinking this supports such a bold idea (that there was a time when infectious epidemic disease was not a problem for ancient armies).
According to this theory Hannibal had 40,000 troops.
According to Arrian Persia commanded possibly a million man army when facing Alexander the Great. Does this mean that the Persian army was even more resistant to infectious disease than Hannibal's army? Or is it possible that there are several things involved in the size of an army?
I concur with /u/Elm11 - this theory would be dismissed by all the historians and institutions I am familiar with.
A related followup question if I may --
I recall reading in print some years ago that modern (post-industrial revolution) nation-states are able to mobilize a far greater portion of their population and economy for total war, and for longer periods of time, than older civilizations. I wish I could remember the source I read it in, it was non-fiction, but perhaps more in the "popular history" genre, which I tend to try to apply skepticism when I read.
I recall at the time wanting to follow up on that and determine its accuracy - can any of our may experts here here comment?