You do have a choice, and it is called Cultural Takeover.

Planets conquered through influence retain their populations.

If you go to war and use force to invade a planet, billions will die.
But violence is not the only option.

1)War Balance trashed.

So you capture a planet, then use its population to fill your transports to capture another ...

2) Economic Balance Trashed.
The war is economically damaging. The troops you move in transport and loose are money you loose. Also, it will take time for the new planet to be economically OK. (or if you micro manage, you can bring citizens from other planets). If the pop would be preserved, the war as it progress would bring you more and more money, thus inflating the war exponentially.

3)Devlopment Time wasted.
Too much change in the game design. I mean, instead of putting HUGE amount of time to redesigning the whole pop cyste, AI, and interfaces, the dev should put their time in something which would make their time worth more.

There's a problem to non-genocidial invasions of planets, and that's assymetrical warfare. A planet is really big. Really really big. There's going to be at worst a billion combatants and billions more saboteurs fighting your army. There's only one way to solve this- massive application of force such as orbital strikes, or converting the populace (cultural and/or information warfare).

In orbital strikes, there's a massive, massive amount of damage done. Or even less techy, imagine a vietnam-like fire team moving up a block, kicking down doors and investigating for rebelliousness or enemy soldiers. Repeat this- five million times a day. There will be collateral damage. A lot.

Further, the ecological and economic consequences of an entire planet being invaded will be terrifying. The defenders will probably use scorched earth tactics, and the offensive side will bombard the hell out of any terrain they can for the advantage. Invading a planet is a very, very messy business. The fact that in a week it's over is way oversimplified. Even the Gulf War took longer than that.

Myself, I like to imagine that troop numbers are divided by 100, producing invasion ships made of 5 million troops per module and that there's a lot of collateral damage explaining why the planet dropped from 5 billion to 0.2 billion residents post-war. If it really matters that much to you, grab a few cheap colony or troop transports with you on the invasions and dump some populace from another planet there to simulate survivors.

Also, population figures in Gal Civ 2 represent how many people are active in the economy and paying taxes. Population figures are not supposed to represent the literal number of people living on a planet. So after invading a hostile planet it only makes sense for the population figure to be small because your economy on that planet is going to be miniscule. If you're worried about realism, it isn't realistic to have a planet you just invaded up and running at anything near 100% its pre war tax base, or even 50%. As people have mentioned, war is supposed to be expensive, and conquered planets should not be able to immediately finance further invasions with money and population.

The diff between military and cultural conquest is too extreme.

Too extreme?

It is the difference between sending in the troops to kill all who oppose, and waiting for the planet to join you of their own free will.

So just how can it be too extreme, when the methods are polar opposites?

I think your misinterpreting him. That is not the way he wants to play Gal Civ. He is bringing up CIV 4 to prove a point.

ROFL!

That was SO funny.

That is not the way he wants to play the game?
Then, find a different game.

I did not misinterpret anything. He wants to invade a planet without losing the population of said planet. It is unrealistic to the extreme, both to think that the general population would not be fighting to the death an invasion by hostile aliens, or that those hostile aliens would leave those they are conquering alive to fight from within after the takeover.

Bringing up a different game to make a point is silly.
Go play that game if you like the mechanics better. I like the way GalCiv2 is set up just fine.

As it is, there are several ways to victory. Invading a planet is destructive, culture flipping is not. Take your pick.

Or even take a look at our own history. WW2 for examle. Germans didnt kill civil population when it didnt try anything like sabotage.

Right, Germany never bombed London.

You are making up story lines in your head, and expect the game to follow along.

It is not me that doesn't get it.

Yup.

You noticed, huh?

Serenity now said it best,

You are both arguing over a point of view about invasions when the actual value of population is calculated as "taxable" population. Whether a peaceful invasion occurs (if thats even possible) or mass destruction can be explained as:

1) Almost everyone is killed. There are very few people "left" to pay taxes or hop onto a transport to invade other worlds. It takes time to "replenish" the population.

2) Very few people are killed. There are very few people "willing" to pay taxes or hop onto a transport to invade other worlds. It takes time to "win over" the population.

I think there's actually a fairly simple sollution to this problem, it does however require a UI change. Instead of just listing the amount of population just list both the total population but add a number that displays the amount of taxpayers/soldiers. You could just list a fixed percentage of population as soldiers.

For example: The planet Earth: Pop: 40.000.000.000 / amount of soldiers/taxpayers 12.000.000.000. This way you don't really have to change any game dynamics and you still won't have to slaughter every enemy planet to the last inhabitant.
You could even ad a bit tot the battle display window about the ammount of inhabitants surviving the invasion. You could also calculate a random bit of no taxpayer dying just to add a bit of flavor. Not to mention the possibility to ad a bit more humor into the game.

End of battle display.
Troops destroyed: 12 billion.
Troops lost: 3 billion.
Buildings destroyed: 1
Civilian population destroyed 2 billion, strangly enough they where all telphone sanitizers, lawyers, marketing execs.