But let's also not forget that one tends to lead to the other, for very good reasons.

Forced collectivization under Stalin happened because voluntary collectivization of the countryside was a complete failure. Marx would not have flinched to use violence in order to seize the means of production. Or how do you interpret this:

“there is only one way in which the murderous death agonies of the old society and the bloody birth throes of the new society can be shortened, simplified and concentrated, and that way is revolutionary terror.”

...

"We have no compassion and we ask no compassion from you. When our turn comes, we shall not make excuses for the terror."

...

"A revolution is certainly the most authoritarian thing there is; it is the act whereby one part of the population imposes its will upon the other part by means of rifles, bayonets and cannon — authoritarian means, if such there be at all; and if the victorious party does not want to have fought in vain, it must maintain this rule by means of the terror which its arms inspire in the reactionists. Would the Paris Commune have lasted a single day if it had not made use of this authority of the armed people against the bourgeois? Should we not, on the contrary, reproach it for not having used it freely enough?"

And there are many, many more quotes which show very clearly that Marx intended for violence to be used to reach communism.