Population

Also I think it is odd that in order to capture a planet you need to decimate the entire population... Shouldn't you be able to win without killing everyone?

Not true, culture it and they flip to you. But think about it. If a bunch of aliens tried to invade Earth, screw the fact that I can't get into the army, I'd help in every way I could, be it running messages, planting bombs, or if it came to it, fighting. Think of the end of Germany in World War Two. There were 14 year olds brainwashed by the Nazi's, fighting against the Allies who they believed evil. Often troops had to kill them, because they wouldn't surrender and posed a constant threat. Same when the Americans went island hopping, a lot of teenagers had to be killed because alive they were dangerous. Anyone who disobeyed the order to shoot could be court martialled. They were fighting for their country, but we're talking about a planet here. Pass me the rifle already! Gotta kill Drengin scum!

Just so you know, I'm not comparing a game to WW2 in a real sense, I'm merely saying the principle is the same. In a last stand, men women and children old enough to hold a gun will fight and kill for their nation/planet.

and anyone to young or old to hold a gun gets killed in the crossfire.

and anyone to young or old to hold a gun gets killed in the crossfire.

The home guard had people over 70 I believe. As for the young, carpet bombing doesn't discriminate. Nor do many tactics.

Anyway, pop isnt overall pop, it's taxpayers. People over 18.

Yeah... brutally raise the tax slider and watch your pop. disappear.


Old enough to vote, old enough to join military service

The population is generally made up of civilians that don't work for the government (you) so you only get tax money out of them really. The money that goes into your production is payment to keep them running as in paid laborers and resources etc. Of course such a large private sector would probably encourage things like technology to move faster in your society, I don't mind that it doesn't have a direct impact on your government projects. After all if a company researches and builds you a new aircraft, the only difference is that you outsource it completely and that's what happens when you magically buy a large spaceship in a single week / turn.

High populations also affords you a larger pool of people to draft into the army during a war and makes a planet harder to conquer both with military force and cultural influence.

The number only refers to the tax payers of working age in your civ and so you don't really kill every person on the planet. While it is a bit excessive to kill even everyone from ~18-65, you can imagine that even if you imprison or hold people under lock-down that they aren't happy, working, productive members of your society immediately. The following growth of your planet can then be imagined as them slowly accepting your government and way of life rather than soley babies being born. Since your population growth is affected so much by approval rating, you can also assume that immigration and emigration are factors too. A lot of people would leave their homes on a planet being invaded if they had somewhere else they could go. Information warfare comes into play also, if they don't like their government / culture / etc, they can rebel with you during the struggle, but if they are happy, they resist.

Of course it's not perfect. I wouldn't mind some expansion on the planetary invasion scenario, but at the same time, there is only so much they can do to 'reasonably' simulate it when the game focus much broader than a single planetary invasion. Planetary bombardments and maybe using multiple invasion options would be nice, but in the end, its a game. The is game balance to consider and on a real time table of a planetary invasion, you'd could probably spend game years trying to take one medium sized planet...

Anyway, pop isnt overall pop, it's taxpayers. People over 18.

huh... I start the taxation of my subjects at 8...
...the way I see it, as soon as they're old enough to sew shoes together, they ought to be pitching in for the Imperium. 80% taxes... oh yah baby, "We love Leader!"
I mean yeah sure, I only have so many state of the art Industrial Complexes built soley to build up my military juggernaught. But let me assure you, my excess population not laboring in one of these specially constructed Building complexes is NOT just here for voluntary conscriptions. No sir, they work in "normal" factories producing all kinds of goods and services for the everyday needs of my people, contributing towards their quality of life. They're payed well for this behind the scene work and each and everyone in turn contributes generously to the Imperial War Chest.

...though, it would be nice to cram a few more people into the local industrial complexes. I suppose if we employ more children at younger ages we can fit more along the assembly line. Food for thought Original Poster!