Right, and the part you quoted is in the context of what immediately followed. The clarification that he was talking about the eventual ideal, and that in the meantime, using authoritarian measures were necessary to the point that anyone who opposed them was supporting reactionaries.

It should of course be noted that Marx expected a spontaneous, worldwide revolution, starting from the most developed countries. This was something that he got completely wrong, (he was not a prophet) and the socialists who put his ideas into practice had to adapt to the real circumstances that they found themselves in. In the case of a worldwide revolution, of course it would be easier to persue the phasing out of authoritarian measures sooner, since they wouldn't be necessary to protect against foreign threats and subversion (something presumably included in the not-yet-destroyed "social conditions that gave birth to the political state"). Even in such a scenario, Engles was extremely clear that he considered such measures absolutely necessary.

What "respected historians" are you referencing? I haven't seen you cite any. Care to share with the class?