I don't think that the map of Galciv II leaves enough options for a tactical planetery invasion as described above (plus it would be very time consuming). However the Galciv I model could be built upon greatly. We need a system by which a ground invasion could potentially last for months.
There are three types of soldiers in Galciv II. These are drafts, regulars and irregulars.
Regulars.
Drafts.
Drafts are troops that are drafted in from the local population, either beacause they were conscipted or have volunteered for the honor of serving ones civ in the army. Every planet has a militerism percentage, which sets the amount of the civilizations budget spent on militerising the population to serve in the army. The key here is that the militerism percentage represents how much of the population is in a fit state for militery service. However the more militerised the population is, the more it will cost to increase it further, so if you want to turn your planet into an armed camp, your going to need to bring in some cash from elsewhere. Reducing the militerism bar below 50% causes militerism to reduce, increasing it over 50% causes it to increase. You can try to keep a very low level of militerism, using draftables only to replace the garrison, or you can try and mantain a high level of militerism and use drafts in combat. Drafts fight reasonably well in battle against other drafts and militia, but fare badly in prolonged battles against regular armies. Militerism is the percentage of the available population that become drafts if a planet is invaded.
Regulars
Regulars are the proffesional standing army of a planet. In order to recieve regulars you will need to construct barracks. Each barracks support 100 million regulars. Regulars are highly trained and well equiped and will mop the floor with lesser troops if deployed in anything like significant numbers. However regulars are costly, in addition to the cost of building barracks, barracks also require mantainance. Mantaining large armies of regulars will require a substantial economy, something not all will have. The homeworlds of all races start of with a barracks, this represents the established martial traditions of those worlds, something which will not immediatly become established on a new colony. When a planet falls, all barracks on the planets are considered demolished in a final act of defiance by the defenders.
Transports
Transport should be able to take a percentage of the local garrison, the regulars on board and/or a percentage of the draftable population. The key here is do you want a small elite attacking army or a horde. A small elite regular army takes fewer transports but requires militery complexes to be mantained on the planets. To complicate matters if you load regulars onto a transport, they still count as mobalised population on the planet, which isn't the case for drafts. A certain percentage of the local population, determined by the draft level of the planet can be loaded onto the transport. However in the process the militerism level of the planet is reduced. Loading large numbers of drafts is a good idea when you have a large expendable population, lots of spare transports and little time, or money to spend building up regular armies. It is often a good idea to load up hordes of drafts alongside regular troops in order to soak up defender bombardment, acting as cannon fodder to save their betters from harm.
Militia and civilians
The population that is not turned into drafts becomes civilians. These are dead weight and they do not take part in the fighting. However they do take casualties from "colateral damage" inflicted by attacking forces. The colateral damage level is usually fairly low and is determined by the following. Generally drafts inflict more civilian casualties than regulars as they are less accurate (but this is determined by morality, see below)
1. The invasion tactics used by the attacker, indiscriminate Weapons of mass destruction can kill possibly more civilians than they do soldiers due to collateral damage levels.
2. The morality of the invader, note this only counts for basic collateral damage levels, not that inflicted by special invasion tactics. The gooder a civilization is, the more gulf their is between the collateral damage rates of regulars and drafts (as civilian are killed by "accident", Drengin think nothing of wiping out the civilian population of an area, however experianced they are, indeed reducing the population to a manable size is well thought of in Drengii.
Irregulars
Irregulars are a rag-tag collection of poorly trained and poorly equiped troops hobbled together as the last line of defense of a planet. Basicly every turn a random number of the civilian population, increased primerily by courage, then by loyalty, then by soldiering ability and finally by planet morale and transferred from the civilian categary to the militia categary. Militia have little attack, but a defense skill which is actually equivilant of regulars. This represents the fact that such forces are usually well-hidden and have to be hunted down in a prolonged guerilla campaign. Typically good civilizations fighting against evil civilizations gain more irregulars, this is to make up for not bieng able to use certain invasion tactics (to represent the populations determination never to submit to their enemies). The reverse is true.
Morale bar
In a planetery invasion both attackers and defenders have a morale bar. The morale bar is determined solely by courage, loyalty and morale (planetery morale for defenders, average civ morale for the attackers). Good civilizations, due to their determination never to surrender have a considerable morale bonus, so good populations can be expected to hold out against evil civs for a long time. This is to make up for the good civs inability to use certain invasion tactics. The reverse is also true and evil civilization has a reduced morale when fighting good civilizations in defense of their own planets. This represents the fact that a good civilization can call upon internal divisions in the evil civilization and inspire the oppressed among them to rise up, often without even intending it.
