Marx actually got what we notionally consider "capitalism" conflated with "mercantilism".

The basis for the Communist Manifesto was not wrong. Factory owners and nascent industrialists in the early days of the Industrial Revolution both in Europe and in the United States WERE exploitative of their laborers. One only need consider tragedies such as the Triangle Shirtwaist Fire in 1911 to see that.

Where Marx failed was in realizing that what the industrialists were in the 19th century the heads of national joint stock companies (e.g., Hudson's Bay Company, British East India Company) were in the 18th century: mercantilists hell bent on permanent transfers of wealth rather than capitalistic creation of wealth. Ironically, both Karl Marx and Adam Smith are critiquing the same fundamental economic system--mercantilism--just in different eras.

Because he failed to acknowledge the mercantilist origins of Europe's industrialist class, Marx arrived at an unsustainable solution: simply reverse the wealth transfers. Marx' Communist ideal--which HAS been tried by Stalin, by Mao, by Pol Pot, and by others--was to transfer the wealth of the wealthy to the impoverished masses. It fails because when you have transferred all the wealth away from the wealthy, you still have impoverished masses. It was the realization of this that left the Soviet Union no viable option but dissolution at the end of 1991.

Capitalism--specifically, the system of free markets within a free society championed by Adam Smith--understands that wealth is created by the productive labor of individual men and women, and that the best utilizations of that wealth occur when those same individual men and women are free to direct their labors as they see fit.

Marx' one true accomplishment was to conflate the economic concepts of capitalism and mercantilism. Marx was never an opponent of free market capitalism because he was too sloppy a student of both economics and history to recognize free market capitalism in the world around him. Rather, he was opposed to a genuine economic malignancy--mercantilism--that he decided to call capitalism. Sadly, the world has been persuaded to go along with his epistemiological error.