Hm, already I cannot exactly remember what the stream showed ...
Anyway, here my thoughts for a basic invasion system (and only that; my thoughts about structures to fend of attacking fleets before invasion starts I wrote elsewhere):
- I agree wholeheartedly with the suggestion to allow the player to place his or her capitol! (much requested by a lot of players for a long time now, or is that just my perception?)
- There should be a logistics value for legions, meaning how many legions a single invasion fleet can hold
- A general is a citizen. He should provide a soldiering bonus to legions and increase the legion logistics value for the fleet he is assigned to. A general is destroyed when the fleet he is assigned to (or more exactly, when the transport he is on) is destroyed in space combat or, with a small chance that is bigger the stronger the defending forces are, conducting an invasion. Leveling up gives a general more soldiering an logistics bonus. A general must be assigned to a distinct transport since an invasion fleet can contain more than one. Invasion fleets can invade without a general (but then naturally without the bonuses). A general can be assigned to a planet to boost the soldiering of defending troops. A defending general is killed when the defenders lose.
- Legions are built from Military Academies on planets as is shown on the stream. Legions stay at the planet where they are produced as defenders until fetched by transports. Legions can level up which increases their soldiering.
- Transports are built as usual, but are empty by default (since it's not sure that there are legions on the planet associated with the shipyard). When starting from a planet or shipyard where legions are present the player is asked whether he or she wants to load a legion (or more, if the transport can hold more than one legion and legion logisitics allow). Transports are not destroyed after unloading the invasion troops.
- Military Academies should also be able to train militia (as opposed to the above expressed ideas of population providing automatic militia units), but militia is much cheaper than legions, cannot be relocated, and is weaker (say, some 33% of default legion strength). And cannot level up. That means a planet without a Military Academy is really undefended when it comes to invasion.
- Now to the invasion itself:
- - The attacker places their legions, the defender does the same for their defending legions and militia units. The defending units are placed first, then invasion orders are processed (see below), then attacker units are placed.
- - I cannot figure out the exact invasion logics now, but as I understood the stream the attacker must take over all cities (and the capitol is one of them, on (pop-wise) small planets the only one). So every round of combat the attacker will move their forces towards the cities and the defender will move theirs to counter the attacker, what not necessarily means that the defender places most of their units on the cities. Whenever two or more opposing units meet on a single hex there is a fight that is calculated by taking into account number of attacking units on hex, number of defending units on hex, soldiering of attackers, soldiering of defenders, defenders' morale modified by population approval ("resistance"), general bonuses and all I forgot to think of now. The structure on the hex is destroyed by the fighting (except cities) and the surviving troops fight on the next round. Units can survive partially what is modelled by decreasing the soldiering of the unit accordingly.
- - Invasion is over when the attacker has a unit on every city (attacker wins) or when that's not possible anymore (attacker has less units left than cities on the planet; defender wins). That also means that an attacker unit is tied to the respective city when they have won a city fight.
- - Buildings should not be destroyed automatically, but only when the attacker and defender meet each other on a hex to fight, because normally the attacker is interested in taking over a mostly intact world.
- - Special orders can be given at the beginning of the invasion:
- - - Destroy every building on your path: legions stop on each hex with a structure for one combat round even if no enemy unit is present to destroy the structure on it. That order can be given in addition to all following orders.
- - - Planetary bombardment: let the player decide how many shots from orbit are fired on the planet between certain limits (e. g. 10 to 50 in steps of 10). The shots randomly hit a single hex and there is a chance to destroy the structure on it, a defending unit on that hex is partially destroyed (soldiering reduced), there is a chance to annihilate the hex (then all units on it are destroyed automatically; capitol is excluded for game mechanics reasons). Every hit on a hex with a structure reduces pop by 5%, if it's a city then by 15%.
- - - Information warfare: soldiering of all defending units is decreased by 10% (communication disruption) and every defending unit is randomly moved one hex away from it's designated starting position.
- - - Tidal disruption: all land hexes adjacent to ocean are impacted as if hit by planetary bombardment (see above).
- - - Core detonation: all hexes are impacted as if hit by planetary bombardment (see above).
- - - Biological Warfare: soldiering of all defending units is reduced by, say, 33%. Pop is also reduced by 33%. Doesn't work against robots or silicoid races.
- - - Plunder: the attacker concentrates on plundering, not on invading the planet. For every research building an attacking unit enters without fight the attacker earns 5 research points multipled with level of structure plus sum of research adjacency bonuses that are deducted from the defenders research points, for every wealth building the attacker earns 5 credits multipled with level of structure plus sum of wealth adjacency bonuses that are deducted from the defenders credits (letting the balance become negative if there are not enough savings), for every manufacturing building the attacker earns 5 credits multipled with level of structure plus sum of manufacturing adjacency bonuses that are *not* deducted from the defenders credits (since manufacturing is not a global resource, manufacturing points cannot be channelled away so that stands for assets stolen and sold for money), for every structure that needs resources there is a chance (say 33%) that the structure is destroyed and the resources needed to build the structure are stolen by the attacker. Approval, influence, tourism, population buildings cannot be plundered, but cities (are there levels?) can provide 10 research points and 20 credits per level, a capitol the double amount, the empire capitol five times this amount. At the beginning of the invasion the player determines how many combat rounds the plundering should last, if after that number of rounds there are still some attacking units alive then those return to the invasion fleet with their booty. If no attacking units survive that many rounds the attacker gains no booty. All numbers are subject to balancing.
- - I agree that ideology should play a role during invasion, but it's getting late and I have no time to figure something out right now. Only thing I can think of right now is an order for malevolent factions to erase the population down to 1 billion to minimize rebellion chance (see below).
- After the invasion damaged units will survive (and get back full strength) with a probability that is equal to (100% - soldiering damage in %). So a unit that got 30% damage during the invasion survives with 70% probability. The winner of the invasion battle is guaranteed to have at least one unit left (which can be a militia unit, even when there were defending legions).
In case of a normal invasion that the attacker has won they can decide how many of the survivng legions stay on the planet as occupation force, but it must be at least one, otherwise the planet instantly reverts back to it's former owner.
- In addition to influence calculation there is a chance that an invaded planet rebels shortly after invasion. The probability for that is something like (1 - 1 / (1 + [remaining pop] / [number of occupation legions] / 10)) * (10 - r/id)*10% with r = number of turns after invasion (starting with 0) and id = ideology difference between attacker and defender (same ideology = 1, maleveolent against benevolent = 3, all other combinations = 2) and is calculated until probability reaches 0 (so if planet is from enemy with same ideology than the chance to rebel is calculated 10 turns, while at max ideology difference the calculation is performed 30 turns).
If the invader adds or removes legions during this period than the calculation is adjusted accordingly.
The planet can otherwise be used as normal (to make things not too complicated).
If planet is taken back by the original owner during the period this calculation is still performed then there is no rebellion chance against the original owner, otherwise the planet is treated as if it belonged to the invader all along.
Referring to tech research times: the longer, the better. Best: it's player adjustable. But that's just my personal opinion. Although research times should never become so short that a tech isn't used at all because it makes more sense to wait for the next, better tech.