Was curious because this sounds kinda weird out of context, especially with a Marx drawing that makes him look like he’s enjoying the idea of causing terror. Here’s what I found find from a brief search:

https://old.reddit.com/r/Marxism/comments/r0ecob/what_do_you_make_of_marxs_quote_when_our_turn/

OP of the reddit thread posting the full quote:

“We have no compassion and we ask no compassion from you. When our turn comes, we shall not make excuses for the terror. But the royal terrorists, the terrorists by the grace of God and the law, are in practice brutal, disdainful, and mean, in theory cowardly, secretive, and deceitful, and in both respects disreputable.”

One of the replies:

The more context here is that Prussia had sent soldiers to shut down his newspaper and he was pissed off about it - this was published in the final issue (in red ink!). So the main point is that he’s condemning the State’s suppression of dissent through violence and throwing a threat in there. And it is certainly true, as in the Twain quote above (and more recently the argument is made in Zizek’s Violence) that the far greater terror of the capitalist state is ignored, treated as unremarkable and inevitable.

I think it is a mistake to take it as a core tenet of Marxist thought, it’s like the 1849 equivalent of him posting a guillotine meme. And in any case, it is wrong. The terror that comes with our turn is a disaster, and we should do everything we can to avoid/minimize it. Terror, no matter who it is directed against, is not an effective way to start a classless society.

Mexie has a great video addressing this here: https://www.youtube.com/watch?v=vVQSKciU4uY along with the follow-up.

Then a slight disagreement replying to that:

I think the point here is that terror is inevitably required when it is “our turn”. The abolishment of capitalism and the revolution it heralds will undoubtedly be violent. Nonviolent action will not defeat the ruling class, as they will show no mercy in defending their existence. Of course the terror is bad, and of course it should be minimized. But Marx is saying that when it inevitably happens we shall not hide it or make excuses. We will own up to it, unlike the capitalists’ deceitful cover up of the terror they have invoked on the world for centuries.

Someone else also highlighted the Twain quote about “terror”:

There were two “Reigns of Terror,” if we would but remember it and consider it; the one wrought murder in hot passion, the other in heartless cold blood; the one lasted mere months, the other had lasted a thousand years; the one inflicted death upon ten thousand persons, the other upon a hundred millions; but our shudders are all for the “horrors” of the minor Terror, the momentary Terror, so to speak; whereas, what is the horror of swift death by the axe, compared with lifelong death from hunger, cold, insult, cruelty, and heart-break? What is swift death by lightning compared with death by slow fire at the stake? A city cemetery could contain the coffins filled by that brief Terror which we have all been so diligently taught to shiver at and mourn over; but all France could hardly contain the coffins filled by that older and real Terror—that unspeakably bitter and awful Terror which none of us has been taught to see in its vastness or pity as it deserves.” ― Mark Twain, A Connecticut Yankee in King Arthur’s Court

So, as far as I can tell, the context is that Marx is speaking directly to the ruling classes who were in the middle of repressing him. And his point seems to be that in the act of deposing them from power, a class who relies on brutality to rule, he will have no compassion for them in that moment nor make excuses for what is necessary to depose them as they so often do for the brutality they exercise to stay in power.

In other words, he is not in it to repeat the deceitful patterns they do and be shy of required violence, but work to get the job done swiftly with honest intention, so that a new society can begin without their terroristic grip in charge.

I am open to disagreement on the interpretation, but I wanted to go over it because, as one of the reactionary replies on the thread I found exemplifies, some people would seize on this as an excuse to characterize marxism as wanting to cause terror in some general way, no matter who is terrorized. Which is quite a different thing from recognizing that violence is an inevitable part of deposing a power that has a monopoly on violence and violently represses those who oppose it. Or not having compassion for the rulers of colony and empire who order massacres and organize genocides.