Just thought i'd pop in with a few references from the old Panzer General which seems to be the base model for the game.
Combat and damage:
All units have 10 Strength as standard. Units could get up to 5 levels of xp, which would cause it to deal more damage and other stuff, but also allowing it to get an additional strength per level.
When 2 units go into combat, they roll for initiative, the winner gets to deal damage first, then the loser deals damage. For each free Strength the init has remaining it gets an attack chance. Each attack could result in 3 results:
Miss, didn't really do anything.
Kill, you removed 1 unit of Strength from your opponent.
Suppressed, prevented 1 unit of strength from your opponent from getting an attack chance.
The chances for the different attack outcomes were determined by the attack value of the attacker vs. the specific unit type and defense value of the defender, ofcourse experience, terrain and fortification also played in.
Retreating:
After both parties had dealt damage, a check would be made on the defender, if they had no free strength remaining (because they were dead or suppressed), they would try to retreat to a nearby tile. If no tiles were vacant they would surrender. The attacker could never be forced to surrender in this manner, since they just fall back to the tile they were in before attacking.
Entrenchment:
Leaving units several turns in the same spot would give them considerable bonuses to defending. How much you could entrench yourself would depend on your unit-type and the terrain you were in. For every battle you fought in, your entrenchment level would also get reduced, representing that your fortifications were getting shot up. If you were forced to retreat, you would ofcourse lose all entrenchment you had. Attacking nearby enemy units, did not cost you any entrenchment (but didn't build any either).
Defensive Artillery:
Artillery filled several roles, first of all, if you tried to attack a position which had backup from artillery, the artillery would get to fire a round on your attackers before normal combat would be resolved. While this rarely gained many kills, having half your unit strength suppressed before combat began would mean your damage potential was effectively halved.
Offensive Artillery:
Artillery could also be used offensively to soften up enemies, but any suppression incurred in such an encounter would not carry over to any "melee" subsequent fights, so mostly this was to get the single 1 or 2 kills, while costing them a level of suppression.
Unit types:
As mentioned earlier, all units have different attack values against different unit types. For Panzer general it was split between Air, soft and hard targets. Infantry, artillery and anti-tank was mostly soft targets while tanks were hard targets, planes were air targets, but while flying units were an important part of PG, they are not really for ciV, so i'll skip those for now.
Transports (the actually relevant part for this topic):
You could equip your infantry with transports. Either at the start or the end of your move you could embark or disembark, but not both. So if you started outside your transport, you could get into the transport, and then move around, but that meant you had to end your turn in your soft transport. If you started in a transport, you could drive up to the enemy, dismount, then attack. I'd imagine the same would be the case for ciV, So having a dedicated navy ready where you opponent is trying to cross water tiles, could potentially devastate his army with no risk to you.
Another thing to note in this scenario is that you don't automatically embark/disembark. So you've landed a few units on a hostile shore and attacked a bit (but obviously not enough). Your troops now have their backs to the water, so if the opponent attacks and forces a retreat, with no other vacant tiles available, your unit will be forced to surrender.
You could ofcourse have left them on the shore, in their transports, allowing you to retreat to the ocean, but the result would most likely be that the enemy simply took advantage of your vulnerable state, inflicting serious pain on your units at no risk to themselves and pushing you back into the sea, so the next turn you start with a wounded army that isn't any closer to capturing that beach.
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