Trade has existed for as long as humanity has existed, correct, but trade isn't Capitalism. Capitalism specifically emerged from Feudalism. The historic ability for a class of property owners to employ wage laborers was only made possible through advancements in production.
To give an example, the feudal peasant largely produced most things they used, from clothes to housing. They would produce excess for their feudal lord, and some small handicraftsmen and guilds formed specialized labor. These were not Capitalist formations, but pre-Capitalist.
Eventually, technological advancements like the steam engine appeared. This revolutionized production, and gave huge rise to a class of owners that could purchase this new machinery, and employ workers in wages to create commodities. The barrier to entry is progressively lowered skill-wise, while the barrier to entry in the market as a Capital Owner raised, as firms began to solidify into factories. This coalesced into a marketplace of wage laborers selling their labor power to various Capitalists, eventually becoming the Capitalism of the time of Marx.
Does this all make sense? Engels, in Principles of Communism, summarizes it as such:
The proletariat originated in the industrial revolution which took place in England in the second half of the last [eighteenth] century and which has since then been repeated in all the civilized countries of the world. This industrial revolution was brought about by the invention of the steam-engine, various spinning machines, the power loom, and a whole series of other mechanical devices. These machines which were very expensive and hence could be bought only by big capitalists, altered the whole previous mode of production and ousted the former workers because machines turned out cheaper and better commodities than could the workers with their inefficient spinning-wheels and hand-looms. These machines delivered industry wholly into the hands of the big capitalists and rendered the workers' meagre property (tools, hand-looms, etc.) entirely worthless, so that the capitalists soon had everything in their hands and nothing remained to the workers. This marked the introduction of the factory system into the textile industry.
Once the impulse to the introduction of machinery and the factory system had been given, this system spread quickly to all other branches of industry, especially cloth- and book-printing, pottery, and the metalware industry. Labour was more and more divided among the individual workers, so that the worker who formerly had done a complete piece of work, now did only part of that piece. This division of labour made it possible to supply products faster and therefore more cheaply. It reduced the activity of the individual worker to a very simple, constantly repeated mechanical motion which could be performed not only as well but much better by a machine. In this way, all these industries fell one after another under the dominance of steam, machinery, and the factory system, just as spinning and weaving had already done. But at the same time they also fell into the hands of the big capitalists, and there too the workers were deprived of the last shred of independence. Gradually, not only did manufacture proper come increasingly under the dominance of the factory system, but the handicrafts, too, did so as big capitalists ousted the small masters more and more by setting up large workshops which saved many expenses and permitted an elaborate division of labour. This is how it has come about that in the civilized countries almost all kinds of labour are performed in factories, and that in almost all branches handicraft and manufacture have been superseded by large-scale industry. This process has to an ever greater degree ruined the old middle class, especially the small handicraftsmen; it has entirely transformed the condition of the workers; and two new classes have come into being which are gradually swallowing up all others, namely:
I. The class of big capitalists, who in all civilized countries are already in almost exclusive possession of all the means of subsistence and of the raw materials and instruments (machines, factories) necessary for the production of the means of subsistence. This is the bourgeois class, or the bourgeoisie.
II. The class of the wholly propertyless, who are obliged to sell their labour to the bourgeoisie in order to get in exchange the means of subsistence necessary for their support. This class is called the class of proletarians, or the proletariat.