Most games are won with the total extermination of the enemy, but real life battles usually end with 5-10% of casualties with some rare deadly battles up to 30-50%. That's because real warfare is slow and it doesn't take much for people to lose morale and lose ground.

I'm trying to make a semi-historical game and I really want to respect this reality of war. So far, what I do is that only a fraction of your army can be sent in battle at once. That way, the combat can be kept deadly, but at the end of a battle, you only lose a little percentage of your total army strength. The problem is that you have to do a lot of battles before an enemy army is completely destroyed which feels very grindy.

How would you make battles rarely cause more than 5-10% causalities of an army, but keep a fast pace so that it doesn't get grindy and boring?

I don't entirely understand the problem. Real battles had low casualty rates because one side would flee the battlefield and the other wouldn't necessarily pursue them. So why aren't you just implementing a fleeing mechanic?

2 hours ago, Kylotan said:

So why aren't you just implementing a fleeing mechanic?

Just be careful with that.

When tuning MASSIVE, the software that rendered the battle scenes in the LotR series, in some early versions the soldiers were often running away from fights.  Between the combination of the fear of the opponent's viciousness and the ratio of damage they could do versus the damage they would take, some units decided the best option was to not fight.

"In the first test fight we had 1,000 silver guys and 1,000 golden guys. We set off the simulation, and in the distance you could see several guys running for the hills."

In rome total war, troops have a morale rating which causes troops to run away so battles dont often lead to a total anihalation.

They run away when they have taken too many loses in a short period of time. Getting surrounded also lowers moral so some can break while others on the side are still okay. Seeing nearby friendly units die or running can also effect moral. Being near the general increases moral as does him blowing his horn.

As others have mentioned, this isn't a particularly hard problem at first glance. Institute systems to model what makes this true for the real world - morale and retreat. As a bonus, this also opens up opportunities for players turning big losses (route) into smaller ones (orderly retreat with rear-guard). 

As for how this makes something grindy? If you're looking to history, then simply follow the same - most enemy armies were not "completely destroyed" before their parent state offered terms of peace. If you want to change the tactical concerns, then you're going to have to revise the strategic ones as well.

8 hours ago, Michael Aganier said:

but real life battles usually end with 5-10% of casualties with some rare deadly battles up to 30-50%

You mean on the winning side ??

or in a very one-sided battle that  isn't balanced?(isn't "fair" we would say irl)

9 hours ago, Kylotan said:

I don't entirely understand the problem. Real battles had low casualty rates because one side would flee the battlefield and the other wouldn't necessarily pursue them. So why aren't you just implementing a fleeing mechanic?

I get the army fleeing the battlefield part. The problem is that the losing army, not having had many casualties, always comes back and makes you fight it a lot of times before you "disband" it. If the enemy army loses only 5-10% each battle, then it takes 10-20 battles to destroy. What should I do to avoid having to fight the same army 10-20 times?

5 hours ago, CortexDragon said:

In rome total war, troops have a morale rating which causes troops to run away so battles dont often lead to a total anihalation.

This is a good step in solving the problem. But in total war, most battles end up with 50%+ casualties on the losing side which is far too high. I could make troops flee after 5-10% casualties, but that might be a bit boring. I want to lower casualties to 5-10% without having everyone fleeing the battlefield which I fixed by only sending a fraction of the whole army in battle. But then, it causes a grinding problem: if each battle only does 5-10% casualties, I have to fight a same army 10-20 times to defeat it. How to avoid this grinding?

Most games with morale implement a lasting morale.  Either for the company as a whole, or for each unit.  Losing a battle would cause the company to all lose morale.  So battle lost, the company flees, but now is at 50% or less morale than what they started the battle with.  So if the winner were to engage that loser again, they'd flee even faster.

Or boardgame style, games often have the loser of the battle flipped over, and any subsequent engagements either cause the unit/token/company to either be automatically destroyed, or automatically flee (perhaps with some loss of strength).  Some regrouping phase comes later, perhaps at the start of the player's turn, and the token is flipped back over, representing the unit having regrouped and regained it's morale enough to fight again.

Another way to look at things, is that 'casualties', in games like Total War, don't always represent kills, but people who have fled the battle, and who don't go back to their army.

@Telcontar and @ferrous seem to have the solution. What I understand is that I must make that a faction surrenders to me when his armies are weakened enough or make sure that a weakened enough army just isn't able to keep fighting anymore. A combination of both would make a lot of sense.

I'll have to try how well this plays in game. Thank you.