Okay, I disagree with this just as strongly as I disagree with attempts to say he wasn't Jewish.  Firstly, Marx didn't kill anybody, nor did his ideology.  A bunch of people claiming to be inspired by his ideas killed millions of people.  And given that the German people managed to produce some unquestionably German people who unquestionably actually did murder millions of people, I'm not going to weep for the fact that the Germans are also saddled with responsibility for one of the greatest political philosophers of the nineteenth century.  Beyond that, Marx was born and grew up in Germany with a very limited connection to his Jewish ancestry.  His primary language was German, and this is the language in which he wrote most of his works.  Although he spent most of his later life in England, I've never really heard that he didn't always consider himself to be a German - I'd think, in fact, that living in England would have accentuated that.  While I do think that his Jewish background is important, and make it perfectly reasonable to describe him as a Jew, his German background was substantially more important than his Jewish one.  His own works emerged out of post-Hegelian debates within the German philosophical community, and his greatest influence throughout his life (and for several decades afterwards) was in Germany, where Marxists were far more dominant within the socialist community than they were in most other parts of Europe (Britain, France, and Russia, in particular, had their own, non-Marxist, socialist traditions that were not assimilated into Marxism for a long time, if ever).  Marx was German of Jewish descent.  Being an "internationalist" is a statement of intentions for the future of the world, not of present day identity.