(Part 2) What the 4th Succession War Implies About Population Size

tl;dr? Soldiers in the 4th Succession War died at the same rate (per billion people, per month) as soldiers in World War II.

Per Volume II of the NAIS Military Atlas, the Fourth Succession War left 100 million dead and 600 million wounded from thirteen months of fighting. (The war lasted from mid August 3028 to February of 3030, with three months of inaction in the middle and two at the end.) That's 7.7 million dead, plus 46 million wounded, each month.

Per Wikipedia, World War II lasted 68-71 months during which 21 to 25.5 million soldiers were killed (with 8 wounded for every 7 dead), 29 to 30.5 million civilians were killed by strategic bombing or warcrimes, and 19 to 28 million civilians were killed by war-related famine or disease. Earth had about 2.3 billion people in 1940, with about 2.0 billion in countries which participated in WW2.

• WW2 killed or wounded about 630k to 800k soldiers, or .032% to .040% of participating populations, per month. The 4thSW's 100+600 million dead and wounded, at those rates, would suggest a population of 1.7 trillion to 2.2 trillion for the 4thSW. 
• WW2 killed about 300k to 380k soldiers, or .015% to .019% of participating populations, per month. The 4thSW's 100 million deaths, at those rates, suggest a population of 533 billion to 676 billion for the 4thSW.
• WW2 killed about 970k to 1.2 million soldiers plus civilians, or .049% to .062% of participating populations, per month. The 4thSW's 100 million dead, at those rates, would suggest a population of 162 billion to 206 billion for the 4thSW. 

We know that last estimate is too low. Firstly because the Inner Sphere has at least 450 billion people, and secondly because the 4thSW didn't purposefully attack civilians and industry the way WW2 did. (I notice that the old Succession Wars board game has industry get damaged in about 30% of assaults, though.)

The high first estimate would mean an average of a billion people per named star system, which is difficult to reconcile with other data from the period. It also assumes no civilians were injured, that 31st century weaponry is not more powerful than WW2 weaponry, and that improvements to battlefield surgery have far outstripped improvements to battlefield weaponry.

The middle estimate makes the 4thSW at least as deadly for an average soldier as WW2 was, which seems like something the old developers would do. It's weirdly close to the geometric average of the high and low estimates, which is a bit disquieting because I don't see any reason for it turn out that way (especially if WW2 casualties have been re-estimated a few times over the years). Maybe it has to do with how they arrived at 600 million for the 4thSW's wounded.

Then there's the question of how many worlds actually "participated" in the war. I count significant fighting on only 140 worlds, but others contributed soldiers, others suffered famine because shipping was diverted... all five Successor States participated in the war, albeit unevenly; I'm willing to let it wash, given the countries involved in WW2 didn't participate evenly either.