Usually the way Marxists analyze the difference between systems like Feudalism and Capitalism, the focus is on how production is carried out, and what kinds of property exist. Under capitalism, generally, industrial capitalists who own private factories transform money into commodities (capital and labor, where labor imparts its value on the capital) which are sold back for more money than the capitalist paid (the surplus coming from labor, which isn’t fully compensated). Feudalism is characterized because instead of the principal mode of production being industrial, it’s agrarian and relies on serfs working on their lord’s land for some period of time, then being allowed to work on their own lands.

The fact that the structure of who owns what kind of property is different is very important. In a lot of ways, this change in how production is carried out (what is called the material base) is more relevant in deciding the direction society is headed than how the government is organized (society’s superstructure). The superstructure is shaped by the social relations in the base, but it can only maintain the base.