What percentage of available manpower can a developed state afford to lose before they they experience a collapse in strategic cohesion? [closed]

Question

Please be careful about mentioning real life examples as they tend to distract from the question. Historical examples of states reaching their manpower limits would be useful though.

There's a lot to consider in this question. Some thoughts I've had to bring it together:

1. Each state has a limited pool of available manpower, which according to Wikipedia's List of global manpower fit for military service, seems to be roughly 15% of the total population. I'm using just men here since most countries don't allow women in front line combat. I'm using a big assumption that the majority of soldier casualties will be combat units.
2. Modern armies have a tooth to tail ratio that means each combat soldier needs so many support personnel to be effective. It appears this is around 15% of the total manpower mentioned above.
3. This does not include how a state's available firepower and hardware affects that ratio. e.g. It's difficult for a state to make advances without armoured vehicles, but they can hold their positions without them.
4. A defending country can of course keep fighting a guerrilla/insurgent war even when the enemy has won by most accounts but I would like to scope this question purely to the ability for that state to coordinate, attack and defend in a conventional combined arms war on multiple fronts and maintain or move the frontlines.
5. Less soldiers can be just as effective as more soldiers on a smaller front, but there must still be a limit. Like 5 soldiers cannot be used as a modern combined arms army. So there is a very rough minimum number somewhere.
6. Economy doesn't come into play here because you can have a great economy but if you no longer have anyone to fight the war, you've lost. The reverse can be said too, but in this question we're focusing on manpower losses only.

Also "casualties" may be a bit ambiguous since an injured soldier could return to the front line. Perhaps it might be best to say "no longer able to serve as a combat soldier". After all even if they are moved to support, the "tooth-to_tail" ratio will shift. I don't know what ratio of recorded casualties, on average, generally become permanent.

I'm looking for answer that assesses the variables involved that add up to a state maintaining it's strategic cohesion while sustaining losses in manpower, or rather adding those up and trying to estimate the limit. e.g. "Considering [n variables], adding them together it seems a modern state could perhaps maintain losses of up to 40-50% of its manpower before it's ability to wage a modern war collapses"

Or to put it better: A state will lose all strategic cohesion if it loses 100% of it's manpower. This is true. However it will also lose that if the state loses 99% of it's manpower. There won't be enough in the military to even call it one or tackle a modern opposing force. So how much do we continue to reduce that percentage until it is effective? Until a hierarchy can coordinate a modern combined arms defense or offense against another modern foe?

Answer 1

I think your question is making a number of assumptions, and I question the validity of much of what you are saying. But let's try to give you some data points that will help you. I think they will mainly show you the problems with the calculation you are trying to make, but I present them anyway.

In World War 1 Germany had a population of about 65 million, which by your calculations gives it a "military service" population of about 9.75m. Total German casualties were around 2m military, 2.5m total, giving you a death rate of around 20% of the "military. They suffered about 4.2m wounded, (can't find out how many wounded were able to continue fighting)so the total "out of action" number may have been 40% to 60%. You could argue that Germany suffered a "collapse in strategic cohesion", but it was probably more about their inability to support the army logistically. Germany was certainly using front line troops outside the age range you are talking about.

By contrast Britain has a 45m population (military service of 6.75m) and suffered 0.89m military deaths and 1.6m military wounded, giving 13% death rate and between 25% and 37% "out of action". Britain suffered hugely but in no way suffered a "collapse in strategic cohesion".

My other data point would be the USSR in WW2. Population 189m (military service 28m), military deaths around 10m and military wounded around 15m. This gives a death rate of 35% and an 'out of action" rate of 60-90%!!!! USSR definitely did not restrict its combat troops to the ages and genders you are talking about. Note that their casualty rate is higher than the German WW1 figure.

For completeness let's do the same calculation for Germany in WW2 - 69m population, 5m military deaths, 7.3m military wounded. This gives us a 48% death rate and between 84% and 120% out of action. German also recruited soldiers from outside the age ranges you mention.

So to sum up the USSR won World War II with a 60-90% casualty rate in its "military manpower" population, as defined by your calculations. This is obviously not a sensible conclusion and I hope it will cause you to rethink your approach.

References: WW1 WW2