"Separation of training and experience. This is realistic and would add motivation to engage in smaller-scale conflicts over smaller goals (kill off some barbarians, pirates/bandits, trade, a node or minor resource etc) that don't necessarily lead to city-scale conquest. There should be a jump in effectiveness and morale for units as they get their first few experience points that tapers off into diminishing returns."
Just wanted to expand on this point a little.
In 4X games there is a reduced tendency to perform small-scale military actions. Occasionally there may be a resource rush or a move to curb bandit activity or something, but for the most part players will avoid conflict unless they are prepared to take a city. There is little motivation to raid enemy trade routes or perform small pillaging raids because the player wishes to build up a massive force and take cities and any military losses before doing so will subtract from this plan or delay it.
This all too often leads to the highly unrealistic scenario whereby a militaristic nation builds up a massive military but does nothing with it for generations (while building up), then takes over the world.
I say highly unrealistic because firstly, obviously, that entire war machine will have no experience. Conquering the world with green troops and inexperienced generals should be far more challenging than doing so with an experienced military that has scaled up its activities from a series of smaller conflicts. Secondly, how does a nation which has ZERO conflict maintain a large military? Even in dictatorships this is politically and economically much more difficult than if there is some justification for spending the money and people. How does such a nation keep up the military's morale? It is possible, sure, but more difficult. This second point is probably harder and unecessary to incporate into game systems, but the first (lack of experience as a practical military drawback) should suffice if adequately implemented.
Smaller conflicts that are worth pursuing to the player imbue play with variety and realism.
How should eperience manifest?
To best achieve these aims, experience could manifest in the following ways:
- Attack and defence bonuses (obviously - soldiers who have fought in real combat have a better ability to attack and defend in real combat than equally trained but less experienced troops. No matter how good your sword training is, the first time your sword gets stuck in someone's skull you won't react as well as the second or fifth time)
- Special ability effectiveness bonus - obviously no matter how many times you train for getting into the Phalanx formation, there is no substitite for that first experience of the enemy infantry crushing into and impaling itself on your spear. Will you puke at the sight and smell of their blood? Or will you efficiently drag your spear out, maintain position and shove it in the next guy's guts?
- Morale bonus - it's well documented that soldiers who have already experienced the heat of battle or the shock of a cavalry charge are less likely to break and run. Morale is very much under-represented in 4X games and this is unrealistic - morale won they day in many historical battles. It also makes sense; the way modern psychologists recommend we conquer our fears or phobias is by repeated exposure to them. Experience improves morale - fact.
- Movement bonus - this is less obvious at first glance, but makes perfect sense. A military unit is not just comprised of troops, it also has a chain of command and logistics support (supply wagons etc). These particularly need experience at moving the unit around and keeping it supplied, and a more experienced unit will always cover more ground in a day's march than an equally trained and equipped less experienced unit. They'll break camp faster, navigate the landscape more effectively, be more disciplined in their movements and experience fewer delays bringing supplies to camp when they stop for the day, etc.
- Supply Bonus (reduced supply cost) - again related to the command structure and logistics part of any military unit. As the unit becomes more experienced at operating in the field under war-fighting conditions, less waste will be observed in the supply lines. The command chain will be better at getting the right supplies to the right troops at the right time, and the guys managing the carts will lose fewer of them stuck in the mud or to thieves. More experienced quartermasters will use up perishable supplies before they spoil, more effectively implement rationing when supplies are low etc. The other side of supply (which needn't be coded for separately) which is of course supply production and long range transport, is ALSO unlikely to be terribly efficient for a nation which has little to no experience in keeping an army in the field under war-fighting conditions.
It's important to note that while an army's commander may well influence all of these things, he or she will also depend on their officers leading and within each separate unit and the quartermasters of each unit for the timely and efficient execution of his or her orders. I'm a line manager myself and I've seen first hand obviously that even the best CEO I could have would be useless if I couldn't implement their ideas effectively. So the commander in charge of an army is important, but so is that army's overall experience, from the unit commanders right down to the poor fools holding quivering spears up to the onrush of bear cavalry.
If you combine these you can see where it's heading. If your nation avoids all conflict for a hundred years but builds up a massive military, when you finally try to take over the world you will be doing it with an army of green recruits who will throw up at the sight of blood, break and run in terror from their first cavalry charge, move slowly and inefficiently through the terrain and cost more to supply due to waste.
This is realistic.
On the other hand if, during your buildup phase, you participate in a series of smaller conflicts for goals that don't directly win you the game (i.e. not necessarily city capture as the goal) then you could go to war with some, most or even all of your units more experienced, more effective, more reliable, more maneuverable strategically and more efficient to support.