I'm just making a new character who's backstory involves having been in a battle - and her side lost and she was wounded.

Considering that's about the extent of that part of her backstory right now (so no specifics) I'm curious what people think would happen to her or other wounded soldiers after the battle when they're found by the winning side. Assuming the winning side are other 'civilised' humanoids like humans or dwarfs etc.

I know there's precedents from history for execution imprisonment slavery or even forcing them to switch sides - but I'm wondering how it being in the world of D&D would effect things - if at all.

It depends partially on who you were fighting. A lot of the Underdark races, like the dark elves and gray dwarves for example, enslave the people they defeat in combat. For other humans or mountain/hill dwarves, I would say just imprisonment is likely. Execution isn't really an option considering...well...your character is alive. Although, a possible background could be that your character was supposed to be executed but through luck, skill, or a merciful executioner was left for dead and managed to survive.

Additionally, something to consider is your characters rank when they were a soldier. How the enemy would treat a captive prisoner is going to change if that person is just a grunt versus an officer or even a noble. Higher ranked soldiers are more likely to be imprisoned for their information, and a noble might be traded back to their kingdom.

I doubt it would affect the big picture, except insofar as some armies would eat prisoners after executing them.  Is your person rich?  If so, they were treated with relative civility by their captors until you were ransomed.  Otherwise, what was the nature of the war?  They might have released you after you swore not to take up arms against them again.  She might have escaped a prison/concentration camp.  She might have been paraded through the streets of the enemy capital then sold into slavery.  If the war is ongoing, there might be a prisoner swap.

The only real difference I would expect from a fantasy world would be things like, who needs slaves when you have magic?  Does the winning side need to stage a mass sacrifice to a god of war?  

Thanks for the replies. I've decided to go with imprisonment for now. Not sure on the duration because I don't know what type of campaign or setting she'll end up in so I'm keeping things vague - leaving my options open to work with the DM later.

For now I'm assuming the nature of the war is two primarily-human kingdoms fighting over land to keep it flexible enough. So imprisonment is probably most likely. She's going to be the soldier equivalent of a sledgehammer so either a basic grunt or other low-rank so she doesn't hold any political leverage.

I imagine the enemy wouldn't hold her prisoner for long because it would be a waste of resources?

Quote from Emmote >>

Thanks for the replies. I've decided to go with imprisonment for now. Not sure on the duration because I don't know what type of campaign or setting she'll end up in so I'm keeping things vague - leaving my options open to work with the DM later.

For now I'm assuming the nature of the war is two primarily-human kingdoms fighting over land to keep it flexible enough. So imprisonment is probably most likely. She's going to be the soldier equivalent of a sledgehammer so either a basic grunt or other low-rank so she doesn't hold any political leverage.

I imagine the enemy wouldn't hold her prisoner for long because it would be a waste of resources?

Well, prisons are expensive.  So I would suspect the only reason to hold you is so you can be used for hard labor to rebuild walls, towers etc.  Otherwise if they feared you, they would just remove your head or banish you, after giving you a lasting brand. 

Or they could have put a spell on you, to never ever pick up weapons against them again.

Prisons are expensive, but you don't want captured soldiers returning to the field against you.  Also, in addition to the possibility of forced labor, captured soldiers could be traded for your own soldiers at some point.

A lot will depend on the nature of the war itself.

If it is a war of annihilation, the wounded will likely be slain unless they have some other value to their captor.  If it is more of a territorial dispute between competing powers, they're less likely to slay captives out of hand with the expectation their troops will be extended the same benefit and that "arrangements will be made" once the fighting stops.

If your character was noble or a person the captors thought was of value, your character might have been captured and ransomed.

Have you watched Star Trek: Deep Space 9?  I ask because there are many instances of prisoners being tortured or mind-wiped or used for experimentation.  In a magical universe, mind-wiping would be even easier and experimentation would no doubt still occur considering that many monsters exist as a result of Wizard experimentation.