Karl Marx died in 1883, so he did not live to witness some of the more longterm successful communist and socialist movements in Europe and elsewhere. In terms of communist movements predating the establishment of longterm socialist states, Marx wrote "The Civil War in France" in 1871 regarding the Paris Commune, which was a short-lived socialist government that governed Paris in March - May 1871. "The Civil War in France" can be read here, but in short it is an address praising the struggle of the Communards in Paris and urging the international working class to learn from the Commune.

If there is any specific movement/party that you are thinking of, Marxists.org hosts a comprehensive and well-organized list of works by Marx and other socialist authors. Do keep in mind that as Marx died in 1883, he would not have been able to comment on any post-1883 communist movements, and any speculation as to how he personally felt about them is just that: pure speculation and hypotheticals.

Wow great information! Thank you to pointing me to some resources. Any idea on the impact the civil war in France had on the communist movement? Meaning, was that seen as hugely impactful or influential at the time? Thanks again.