George Blake Dead

[The Minsky Moment]

In the Manifesto, the proposed measures include state centralization of the means of transport and communication and "Extension of factories and instruments of production owned by the State".  Some ambiguity here, but this formulation appears to presume that significant ownership of factories and instruments and production will remain in private hands.  That is also implied from the proposal to abolish private property "in land" - which suggests other forms of private property would not be abolished. Marx wrote quite a bit more after 1848 but not much that shed light on the specifics of a Communist polity.

[Josquius]

"Marxism" was never a tightly coherent body of political theory.  Marx was a philosophy student turned journalist turned pamphleteer and professional radical and his written work reflects this.  The Communist Manifesto is rhetorical critique of contemporary society  using a vaguely Hegelian historical template and a list of a programmatic demands tacked on, demands that to the extent are comprehensible today are descriptive of a social democratic program.  Capital is a confusing mix of reporting on contemporary factory conditions and an attempt to rework Ricardian economics. His other essays similarly combine reportage and commentary on current events with a mish mosh of political and economic theorization.

It's hard to derive any concrete program from Marx's writings and to the extent he made predictions about the development of European capitalism based on his theory, in the decades following his death, it became apparent those predictions were incorrect or at least badly incomplete. It's no surprise therefore that would-be Marxists ever since have wrestled with this material and differed about its meaning. 

In the early 20th century, revisionism (Bernsteinism) emerged as a dominant force and indeed remains so.  Modern day parliamentary socialist and social democratic parties in Europe are descendants of the late 19th century Marxist social democratic movements and parties that took the revisionist turn - and in this sense it could be claimed that Marxism as revised succeeded. If you look at the few programmatic concretes of Marx - namely the specific goals listed in the Manifesto like graduated income taxation, inheritance taxation, central banking, free education, child labor bans, state control over key utilities etc. - social democratic parliamentary parties in the West made very significant progress towards those goals. While for the most part they did not do so through the kinds of revolutionary transition envisioned by Marx, these political developments unfolded in a manner that could be described using a dialetical metaphor or the metaphor of "contradictions of capitalism"

Revisionism thrived because it provided answers to the obvious fact that worker immisersation was not intensifying in Europe (as Marx predicted would happen as the causal trigger for revolution) but apparently ameliorating somewhat and that workers were making real inroads politically through participation in parliamentary politics, and socially and economically through trade unionism. Lenin defined himself and his thought in direct opposition to revisionism.  It is explicit in "What is to be Done" where the opening remarks present the work as a response and refutation of Bernstein.  Leninism is the mirror image of revision: instead of Marxism being brought to fruition in leading western economies by broad based mass worker movements working through free parliamentary politics, it would instead emerge in "backwards" nations by the leadership of a small elite revolutionary clique operating through revolutionary violence.

Leninism is pretty nonsensical as political theory generally and also as a good faith and just interpretation of Marx, which probably contributed to the historical struggles of the Bolsheviks to attract a mass following (as compared to say the SRs).  However, as a program for seizing power in a chaotic political environment, Leninist vanguardism definitely had legs.  I can see why it would be attractive to frustrated youth and intellectuals desperate to put their ideas into action at any cost and take revenge against their real and perceived tormentors; it also has attraction to criminal opportunists for obvious reasons.  But for a would-be western intellectual seeking justification according to Marxist ideals, there really is no excuse.

Good points overall but I would say to be wary of giving Marx too much credit.
There's a huge strain of belief from the right that Marxism and Socialism are one and the same, that Marx was the founder of socialism and his works stand as the holy bible for anyone claiming to be a socialist today.
Marx was massively important for sure, but he was not the only nor even the first socialist around.
In particular relevant to your post here- revisionist Marxists and the founding of social democratic parties.
In the UK at the least with Labour Marxists were just one of many groups that played a part in the foundation of the party.