This is the part in question, from part I (A) 5. (you can see the whole book here - it's not one of his most accessible works, though:
https://www.marxists.org/archive/marx/works/1845/german-ideo... ), with some inline comments (the quoted text is all one continuous section):
> This “alienation” (to use a term which will be comprehensible to the philosophers) can, of course, only be abolished given two practical premises. For it to become an “intolerable” power, i.e. a power against which men make a revolution, it must necessarily have rendered the great mass of humanity “propertyless,” and produced, at the same time, the contradiction of an existing world of wealth and culture, both of which conditions presuppose a great increase in productive power, a high degree of its development.
This is a recurring theme with Marx: Revolution is not a political goal, _per se_. Class struggle is not something to strive for, _per se_ - it, according to Marx becomes a necessity when (if, but Marx believes it will inevitably occur) the governments of the current system becomes an "intolerable power", and for this to happen under capitalism, it must not just cause poverty, but cause poverty in contrast with greatly increased wealth.
> And, on the other hand, this development of productive forces (which itself implies the actual empirical existence of men in their world-historical, instead of local, being) is an absolutely necessary practical premise because without it want is merely made general, and with destitution the struggle for necessities and all the old filthy business would necessarily be reproduced;
The above is the specific line I had in mind.
You'll note that Lenin spent quite literally years before he succeeded in convincing enough of the (then) Russian Social-Democratic Labour Party that there was sufficient reason to basically ignore this, and that it would be possible to "short-circuit" this process in Russia. In retrospect, of course, we can see just how wrong he was: It took just until the early 1920's until the Bolshevik's had picked up all the Czarist regimes oppressive tricks and started firmly establishing the Party as a new upper class in the face of the consequences of redistribution in a poor agrarian economy, and we've seen that pattern repeated over, and over.
Marx saw a well developed capitalism as both inevitable, and an absolutely necessary precondition for the development of socialism.
> and furthermore, because only with this universal development of productive forces is a universal intercourse between men established,
Global trade. Or to take it to its logical conclusion, globalisation:
> which produces in all nations simultaneously the phenomenon of the “propertyless” mass (universal competition), makes each nation dependent on the revolutions of the others, and finally has put world-historical, empirically universal individuals in place of local ones. Without this, (1) communism could only exist as a local event; (2) the forces of intercourse themselves could not have developed as universal, hence intolerable powers: they would have remained home-bred conditions surrounded by superstition; and (3) each extension of intercourse would abolish local communism. Empirically, communism is only possible as the act of the dominant peoples “all at once” and simultaneously, which presupposes the universal development of productive forces and the world intercourse bound up with communism. Moreover, the mass of propertyless workers – the utterly precarious position of labour – power on a mass scale cut off from capital or from even a limited satisfaction and, therefore, no longer merely temporarily deprived of work itself as a secure source of life – presupposes the world market through competition. The proletariat can thus only exist world-historically, just as communism, its activity, can only have a “world-historical” existence. World-historical existence of individuals means existence of individuals which is directly linked up with world history.
> Communism is for us not a state of affairs which is to be established, an ideal to which reality [will] have to adjust itself. We call communism the real movement which abolishes the present state of things. The conditions of this movement result from the premises now in existence.
This is one of the parts of Marx that is most often "lost": While on one hand Marx had ideas about immediate political goals (his "Critique of the Gotha Programme" is one of the most accessible, short works on that - it was a letter written to tear to shreds a proposed new party programme for a German socialist party), he wrote very little about the "end goals", as he saw socialism and communism not as something to fight to achieve, but as something that will inevitably happen as a consequence of the development of capitalism.