Eh, a quite popular game, Mount & Blade, which spawned sequels (the more polished M&B Warband, upcoming M&B 2) and spinoffs (M&B Viking Conquest, M&B Napoleonic Wars, etc) has "slavery". You can just capture people at the end of each battle. Sell them to "slave drivers" in the cities, which gladly tell you exactly what they do with the people (ask for ransom, if no relative pays up, sell them as slaves somewhere). Literally no actual consequence beyond maybe some companions (iirc) kinda disliking it. But thats it. Its a nice source of gold in the early game.
Everyone knows the primary purpose of mount&blade's slave system was to force hundreds of forest bandits to join you and do a robinhood playthrough. At least that's what I did.
I think why it worked for Mount and blade was because it was a versatile mechanic. It started as a way to make a small amount of money or as a way to gain recruits you couldn't hire. Later in the game the capture mechanic is used to ransom kings, this had it's own advantages and disadvantage as ransom kings could later be recruited by your king creating a enemy or friend depending on your actions.
In the end not many people used the capture system in Mount and blade to make money, because there where a lot of more profitable ways to get money.
Include it, but let "others" deal with it, not the player. This would be dishonest. Slavery wasnt done by only "evil men", it was done by almost anyone and every nation.
Slaves where held by both fair and dishonesty men, however only the cruelest and heartless captured and shipped slaves.
It's believed that at least half if not more slaves died during transportation by sea. Livestock trade by ocean is expensive, even more so when they are fragile two legged humans who eat the same food and can spread disease.
Slaves where often left to starve to allow the crew to eat, the sick where killed to prevent epidemics, the crew was brainwashed and taught that the slaves where less than human to prevent mutinies and the woman where some times used to reward the crew.
Then there was the dilemma of keeping your "stock" in good condition as malnourished slaves would die and with out physical exercise they would be worth less; slaves kept under good conditions rebelled against there captors.
These are hard choices to make, the good people died in the middle of the ocean because they refused to treat people as just commodity for trade.
Include it, but dont make it profitable. Why? It was VERY profitable, this is why it was so widespread. The economic system encouraged it and plantations wouldnt exist in the way it did if not for slaves.
Slave trade wasn't that profitable for the slavers.
Besides the conditions mentioned above, slaves would often commit suicide by starving them self and had to be force fed. Others would throw them self, and there children into the ocean to drown. On land the slaves died of dysentery in the hundreds, tried to escape and rebelled.
In a shipment of 600 slaves only 150-180 would arrive at the destination, in such a poor condition that selling them was difficult.
Things only got worse for the traders when plantation started selling there excess slaves. Plantations needed large amount of slaves to be built however less slaves where needed to maintain the plantation. These slaves where better fed and stronger than the slaves sold by traders.
Then things got even worse as plantation slaves had children born into slavery, these new young slaves where accustomed to living as slaves and were healthy and strong.
In the end actual trading of slaves where done by neighbors and neighboring towns, with actual slave trade accounting for less than 30% of slaves trade.
Keeping idle slaves where considered a risk, so selling slaves where important that is why it was so wide spread because slaves and land was cheap, spreading slavery like a disease.
Considering the fee needed to pay a crew, the cost of repairs and taxes; slave trade wasn't that profitable for traders when better plantation slaves where sold.
Most slave trade vessel bought better trading licenses and others realised you could rob the people your killing and became raiders.
Owning slaves and selling what they produced was profitable, so the rich get richer.
Include it, but make the player "the good guy" by intercepting slave ships and freeing slaves. Really? This NEVER happended and would make a very strange trading game.
When some of the African war chiefs and kings learned how the slaves where treated, they stopped selling there prisoners of war and launched small ships to fight against slavers.
The problem you face is that unless you include every detail of how slavery was you will be misrepresenting how profitable slave trade is.
Considering that slave where less than 3% of the goods sold in the 1600s - 1800s it's not worth it unless the goal of the game is to highlight slave trade.
