I'm mostly agreed with the previous comments. 

Just a point, there is an attrition mechanism, but I seen it only in peace without open borders to a opponent I harassed from the beginning of the game. He was constantly spawning on my lands and slowly died marked as "maimed".

I think the units should have a supplied status with a number, and on ennemy land. It decreased. 

If the units retreats, it also lost all his supply and lost some of his life. Or instantly take the maimed status and can not take it twice, the second time should be a kill like enless space.

Or if a unit flee the combat, the attacking unit does not lost his moving and action points.

Siege should slighty breaks some walls as saping, and these walls should be not passable. So without siege unit, you have to construct ones, like some total war. 

There should be a Line of Sight in deployment for ranged units so that when deploying them you know what they can and can't see.

Combat has improved greatly since my last OpenDev experience. The quicker pace is welcome, and the UI is clearer. I absolutely love how critical terrain is, and how much it rewards smart tactics. 

One gripe: Zone of control. I find it odd how melee units can go all the way around another melee unit as long as they don't separate. This makes protecting your archers an awkward task. I think that units should be unable to 'go around' other units unless of course, they are cavalry. Placing my swordsman in front of my archer, only to have another melee unit travel 180 degrees around my swordsman to hit my archer is just silly. Perhaps this was done for balance reasons, but it certainly isn't intuitive.

To be more clear, I suggest seeing how things look if melee units cannot circumvent other melee units, or must invite an 'attack of opportunity' if they insist.

The combat in civ is one major reason that I never played any Civilization game (except SMAC), so I really appreciate turning it into a little minigame. The way it emphasizes the terrain feels really good, if a bit confined due to the many harsh cliff breaks (especially on this map). Compared to the earlier scenarios, the combat is much more readable and fluent.

What I don't like about it I already didn't like in Endless Legend: That small differences in tech make combat entirely lopsided. Its not as bad as in EL, because you don't need to stockpile strategic resources, so you can possibly catch up better (at all), but having even slightly old units be completely useless does not feel good at all. I would welcome a strong difference between modern and premodern units, but the difference between earlier units should not be that pronounced (and that's before going down the rabbit hole of Roman Legions vs. medieval armies).

As FinalFreak16 stated above, impassable Walls by enemy units until their complete destruction seems very reasonable. Walls need major buff to its current state.

And for the Naval Units, there is little incentive to actually build Naval Units, not only since Naval Transport Units are already quire powerful, but also since Naval Units(such as Boarding Vessel or Gun Platform) are simply useless. (Except for scouting duty). No ability to attack a City tile or a land unit makes the situation even worse. Naval Units need proper incentive over Naval Transport Units...

Cavalry should be changed from a class to a trait. That way anti-cavalry works against ranged horse units (although it should not work when defending against ranged attacks), and ranged horse units can ignore Zone of Control. 

I absolutely LOVE the HK combat system! I have no words to describe how much fun and refreshing it is.

here are some ideas on how to improve it:

1. Show units stats (elevation, terrain, buffs, etc.) like EL icons on the units while in combat.
2. Change the forest tile graphics - it looks like rocks. You can do something similar to EL.
3. Make the battle area boundaries clearer - I would include mountains in the battle area outline and put a disabled symbol on them, creating a more symmetric battle area.
4. Sometimes it's hard to see which cliffs are passable and which are not. no idea how it can be solved
5. Make the battle calculation easier to understand
6. Improve reinforcement UI - make it easier to understand and how to deploy.
7. Improve the retreat mechanism - punish the side that uses it and not the side that it is being used against.
8. Have the option to choose auto-resolve in a better way than a small toggle.
9. Improve the movement/attack line while in battle. It's hard to get out of attack mode sometimes.
10. Explain better how the size of the battleground is determined and what effects it.
11. There is no easy way to cancel future actions (move/attack) for units in battle and on the map.
12. All the UI tabs of the units in battle look like they enabled - there is a small, subtle underline on the tab that is hard to see.

Elephant units should also be considered Cavalry.

I think high ground is slightly too impactful right now. The way rivers are handled is weird too.

However, I think the reason high ground is such a problem right now is that most high ground in the world seems to be a cliff that is inaccessible to melee units on the wrong side. There aren't many plain old hills, rather elevation differences tend to be accompanied by a lot of terrain that also limit your ability to maneuver. I would tone back the cliffs on world gen to create more rolling hills, and reduce the high ground modifier to +3 rather than +4. (as an aside, the number of cliffs feels pretty unnatural as well.)

[Feedback] UI/Icons overhaul for stacked Reinforcement Units is needed!

In Battle, when there is already a Unit on a tile, on which Reinforcement Units are placed, Unit icons become overlapped and hard to select each Unit. Here is an example:This is particularly annoying, if it is zoom-out. As the Unit becomes (relatively) smaller, the icons become even closer or completely overlapped. Hence I would like to suggest UI/icon overhaul for this kind of stacked situation.

For instance: Place Reinforcement Unit icon above the icon of Unit in Battle. To select Unit in Battle, click either the tile or the icon of Unit. To select Reinforcement Unit, click the icon of Reinforcement Unit. Just like the picture below. (sorry for bad quality... I'm not good at 3D/2D art)

Basically this: https://www.reddit.com/r/HumankindTheGame/comments/kk0z2j/combat_adjustment_suggestion_description_in_first/

I'll repost my comments to save a click.

In my experience with the OpenDev so far, I've been surprised on how one-sided warfare is. Once a side gets any meaningful Combat Strenght (CS) difference, it can steamroll the opposition, with little to no damage. Having the warfare be more dangerous to the winning side makes it more risky and gives better comeback opportunities so the losing side is not steamrolled so easily. To address that, I suggest a small change to the combat mechanics. In the table above, you have the damage dealt per blow based on the CS difference. The second column represents the damage dealt to the lower CS unit by the higher CS unit, which I think is fine and should be kept as is. The third column represents the damage dealt by the lower CS unit to the higher CS unit and, IMHO, it falls too quickly, going to the floor of dealing 5-10 damage per hit at a measily 4 CS difference. My suggestion is to increase the damage dealt by the lower CS unit, according to the fourth column, thus making battles less one-sided and IMHO avoiding the one-sided warfare we have on the current build. 

I have to agree retreat option makes for frustrating war. I had no problem with destroying anyone, catching them was a problem that unnecessary lengthened every war. The ransacking of outposts connected to a city was way too easy, quite a few times I was able to do it with only one unit in one turn, often breaking the huge city into several unconnected outposts, had the same happen to me on occasion, when enemy managed to sneak a cavalry unit into my empire. Well sneak is not really good example as most of my armies had 1-2 movement only due to retreat mechanic. At the end I had decided to forgo any unit that was not cavalry as otherwise it was not possible to catch any enemy. That said 7 movement unit being blocked by attacking adjacent enemy and unable to pursue at all was annoying. I guess best way to sum up the combat at it is would be frustrating. 

I agree with most of the suggestions here.

Walls should have more hp and absorb the damage that the unit would receive that is standing behind it. If there is no unit behind it, take a sufficient value for the tech level (it should be easier to break down a wooden wall than it is to break a stone one, hitpoints just being one part of the equation). Only if the wall is broken down, the unit behind it should start to take damage. That way, placing archers inside the wall would make more sense (they are surprisingly squishy when they are inside walls, despite that being the best place to place them historically and logically). On a similar note: why isnt militia able to do ranged attacks? they are supposed to stay behind walls, where they could chuck rocks and pointy sticks from the wall... The amount of milita should also rise with the town size, something that I havent noticed (I havent been attacked all that much, tbh. either it isnt there, or the game thinks a town of 15 is fine with 2 militia defenders).

I would also suggest that docktorkain's post be upvoted as much as possible. Currently having a slightly better unit means it can slaughter the opposition with no big drawbacks (the little hp lost is quickly recovered if supplied). I do not wish the "spearman beats attack helicopter" nonsense that some Civilisation versions suffered under, but at least give normal infantry a chance to at least dent a culture specific infantry unit.

I'll join my voice to the chorus about the frustration regarding the retreating units.

Especially as this issue compounds with the fact that, given the size of the battleground, all the units in the vicinity of the battle get involved in the battle, even with the retreat... so, if you have a cavalry army nearby to run the retreating forces, they are stuck because "they were involved in a battle"... that is completely wrong.

I can see two solutions:
1. if the the enemy retreats, armies that are not the army starting the battle should be able to move

2. we should be able to say that armies nearby are not to be involved in the battle

I understand those two options have their drawback... but the retreating feature all the time is darn frustrating.

Enemies should spend one turn trying to scale the walls, wasnt it like that in one of the open devs? I wonder why it was removed

I'll come in with some of my own suggestions and echo some of those above.

1. I will echo doctorkain's example on increasing damage dealt by lower CS unit's against higher CS units, though I think the higher damage values should extend a bit further.

2. Currently it feels like there is little reason to not just select the highest CS unit available. I feel like ancient/classical/medieval melee should have more differences in their role, by adding a bit more of a rock, paper scissors mechanic. Perhaps axe/sword infantry get bonuses against spear and ranged infantry, while spears retain their anti-cav function, which of course culminate with the Halberdier functioning as both. I also like Gan1997's suggestion to give light cav and heavy cav different bonuses. 

2a. On a similar note, it feels bad that EU's that replace standard units lose out on the standard unit's abilities, such as Naginata Samurai losing anti-cav. I think we can handle 3-4 traits on a unit, especially an EU.

3. Archers drop off in effectiveness too quickly. Though changing the difference in power calculations could help that, maybe Ancient Era could have slingers, and the Classical Era could get archers? 

4. Gunner comes into play too early. Crossbows and arquebuses would make more sense being regular ranged weapons. Historically both weapons are notoriously slow on the reload, but morseo from a gameplay perspective, it still gives you more of a reason to field Pikemen and Halberdiers alongside Crossbowmen and Arquebusiers. Gunner feels like it'd make the most sense to come online with Musketeers, representing the final obsolescence of melee infantry.

5. LoS for ranged units feels unintuitive to the point where I feel certain that it is not currently implemented correctly in this build. It felt like my gunner units especially could only shoot in straight lines away from any side of their hex, and if a unit was between those lines, then no can do.

6. Sieges feel weird. I like suggestions above that you shouldn't be able to cross walls while within the zone of control for anyone on the inside. Furthermore I don't think cav should be able to cross the wall at all, and that if infantry can, it requires their whole movement, the way embarking does (takes a while to get up those siege ladders after all). Otherwise, fortifications in combat should get a bit of a buff, and/or levies/peasants/etc should. Perhaps defenders next to a wall also get high ground advantage (maybe once you build palisades instead of fences). I feel like these changes would make you more likely to consider whether or not you'll build siege equipment or just storm the walls. 

5a. A tech/infrastructure to make some of your home guard units the ranged unit of the era could make sense to make the battles more dynamic for the defender.

7. Retreating is annoying as all hell atm. It shouldn't deplete an army's movement, I mean all my soldiers did was glare at the enemy menacingly and they ran away. I think there are few things suggested above that would make the mechanic less annoying too, but this is the big one.

8. Naval units that don't have the boarding platform feature (or whatever it's called) should be able to attack units that are within range on land, especially if they have a range of two or greater.

Cav should definetely be able to go across the walls as dismounted troops, but lose strength, speed and cav boni when doing so/being within.

It's also worth mentioning with all these thoughts aside, the biggest problem with combat is getting the AI to face you in a decent battle. Only once did I get into a war with AI where I had some really good large scale battles, and it was a game where I was building up quite slow and they got to the Early Modern Era and Arquebusiers before me. I still kicked their ass pretty good, but a few mistakes or bad strategy probably would've lost me the battle. Probably would've beat me too if it weren't for my Teutonic Knights going into crusade mode against their opposing faith.