This is an exciting question to answer because, in the post-WWII era, there's been a revolution in our understanding of the social and economic structure in the middle ages. I'm going to focus on England, because I know the literature for this the best due to the arguments around the causes of the Industrial Revolution. Also I'm drawing heavily on answers I have written before on r/Askhistorians on similar questions. 

The term "capitalism" was first used in the 19th century, as a label for the existing economic system in the UK and other similar countries.  This was a time when historians and economists talked about "feudualism" as a distinct system of economic organsiation that had covered much of Europe in medieval times. Karl Marx used the term "feudualism" extensively, and contrasted it with capitalism, viewing the two as having very distinct economic systems, with capitalism having replaced feudalism in a revolution where the bourgeois displaced the aristocracy. Marx's intellectual influence has been huge, and many writings in the 20th century, and even now, draw on this conception of there being something distinct about the economic system of the UK of the 18th-20th centuries, compared to earlier times. 

However modern historiography, drawing on research carried out since the 1950s, has a very different view now of economic organisation in medieval Europe. Generally, a lot more complex one that emphases variation between different places and variation in organisation at the same places at different times. In the case of England, the medieval economy is now regarded as highly market-based and accounts of the Industrial Revolution talk more about a gradual change. To quote the economic historian Gregory Clark:

The more we learn about medieval England, the more careful and reflective the scholarship gets, the more prosaic does medieval economic life seem. The story of the medieval economy in some ways seems to be that there is no story.

Back in the bad old days, when the scholarship was less careful, the medieval economy was mysterious and exciting. Marxists, neo-Malthusians, Chayanovians, and other exotics debated vigorously their pet theories of a pre-capitalist economic world in a wild speculative romp. But little by little, as the archives have been systematically explored, and the hypotheses subject to more rigorous examination, medieval economic historians have been retreating from their exotic Eden back to a mundane world alarmingly like our own.

(Okay, Gregory Clark sounds a bit more depressed than excited).

And this view isn't just applicable to the middle ages, economic institutions like wage labour and land ownership can be traced back to Roman times, and even earlier, the earliest I know of is 4000 years ago. The Hekanakhte Papers are a surviving record of Ancient Egyptian economic management from 20th century BCE. These papers are letters that a landholder and minor priest, Hekanankhte, wrote on a variety of matters, including instructions to the agent managing his land. He discusses grain and cloth sales, renting lands, debts, and the wages to be paid to various servants (apparently in terms of barley). (Note I am not an Egyptian expert, and am about a zillion miles from reading Egyptian hieroglyphs, and thus am totally relying on secondary literature here). This doesn't tell us of course about how much of the Ancient Egyptian economy was operating on market-based principles versus other systems, but it does indicate the very long history of things that used to be regarded as new to the economic organisation of England around the time of the Industrial Revolution.   There were people calling for more free-market reforms in the 19th century, inspired by the ideas of the Scottish Adam Smith and other economists like France's Frederic Bastiat, but they typically called themselves "liberals", and thought of economic reforms as part of a larger grouping of social reforms to increase individual freedoms, such as abolishing slavery, religious discrimination, married women's property rights, democracy, etc. The Italian fascists of the 1920s and 1930s rejected both communism and liberalism. (Then in the USA in the 20th century the meaning of the term 'liberal' evolved to being more associated with government intervention in the economy and welfare state policies). Liberals could and sometimes did attack ideas that other thinkers have regarded as essential to capitalism, such as colonialism, Adam Smith for example argued that European colonialism was both harmful to the inhabitants of the subject country, but also to the economy of the colonising country. 

Capitalism still gets used today by a number of academics, but I don't find it useful as a term, it means too many things to too many different people, and arguably focuses attention too much on narrow questions like "the ownership of the means of production" while neglecting other things that are connected with countries' economic outcomes, like levels of corruption, or the money supply, or the functioning of the price system.

In summary, post-WWII research into economic history has been such as to totally overturn the view of distinct stages of economic organisation in Western Europe.