What makes capitalism different is that the power is distributed along capital (as opposed to handpicked by the king under feudalism; or embedded in government monopoly under mercantilism).
In other words, in capitalism, the owners of capital (or the owners of the means of production; i.e the rich; the aristocracy; etc.) are the ones who get to dictate the living conditions of the rest of society. The rulers (be it democratically elected government; an absolute monarch; a military dictatorship) will legislate in order to maintain the interest of the owners of capital. The police (or military) will fight for the interest of the owners of capital, and will suppress any resistance against the interest of the rich, etc.