EDIT: Just to narrow down the question a bit, I would like to know, from the perspective of the socialists of the late 19th century, why Marx's ideas could be more convincing or appealing comparing to other socialist thinkers (in the broadest sense) such as Proudhon and Bakunin? I am under the impression that many (competing) schools of thoughts existed in the broad spectrum of socialism. How did Marxism emerge as the dominant one?
This is an extremely broad question, and answering it properly would require at the bare minimum, several pages of writing.
If you are genuinely interested in what made Marx so influential, I would recommend reading up on early utopian socialists (specifically Saint-Simon, Fourier and Owen) along with some readings on the industrial revolution, as well as the history of the Paris commune before moving on to reading Marx. By doing this, you will be able to fully understand the context of Marx's ideas and the enormity of them.