Silk, and in general almost every type of clothing until modern cotton processing. Most traditional clothing was very coarse and one of the most obvious class indicators, across millenia.
silk was so in demand and so lucrative a product that at one point smuggling silk worms out of china was punishable by death. I think the price of a silk shirt in the middle ages was roughly comparable to a luxury car today.
These comparisons always bring up the fact in my mind that the lowest class people today have so much better sanitation, like toilets compared to kings back then
Is there a specific war, genocide, or other event that you were referencing though? I wanted to learn more.
I guess it was the main driver of slavery in the US...