Feudalism was capitalism too. So is slavery. The working participants are part of the capital.

In feudalism, though, Capital wasn't king the way it is now. A lot of the feudal capital (serfs, land, et cetera) wasn't fully exchangeable.

In feudalism the King was the Capitalist. The serfs were the participants.

Labor is part of the capital. The person providing labor is a participant. They aren’t actual capitalists. Many (worker) people have been conditioned to think they matter in capitalism and they themselves defend and protect the actual capitalists. Obviously many working people do very well in the arrangement as it is and don’t want it to change, some don’t want it to change out of fear, some point at other systems as “bad” even though their counterparts in those systems do better than themselves.

I meant to add: in our capitalist system the worker came closest to being capitalists when unions were at their strongest which gave workers more power and control in the system. Probably 1950s - also when tax rates on the wealthiest people were at their highest.

I agree that in actual capitalism, labor is a form of capital. However, real capitalist capital is usually fully alienable, unlike the more fixed and less exchangeable forms of capital under feudalism.

American "capitalism" and wage theft are different things. Unfortunately many in the US are programmed to accept the latter as the former.

How do you define "capital?"

To me, "capital" is the means of production including money, equipment, etc excluding labor. The "capitalists" make the profits in these arrangements. The labor participate in the process and are paid/compensated (or in slavery's example the slave is afforded to live...that is the compensation) for their labor by the capitalists but participants are not in control and do not get profit. Labor is a liability to a capitalist. Not an asset. the labor is an asset of the participant, But they have very little to no control. Their labor is a commodity the capitalists can purchase elsewhere to make more profit.