One problem with this is that the word "communism" generally did not mean the same thing in 1900 it did after 1917:
"Prior to 1918 the word “communism” did not mean Left Social Democracy of the sort represented by the Russian Bolsheviks, a radical, revolutionary form of State socialism. Quite the contrary, it was used of those who wished in one way or another to abolish the State, who believed that socialism was not a matter of seizing power, but of doing away with power and returning society to an organic community of non-coercive human relations. They believed that this was what society was naturally, and that the State was only a morbid growth on the normal body of
oeconomia, the housekeeping of the human family, grouped in voluntary association. Even the word “socialism” itself was originally applied to the free communist communities which were so common in America in the nineteenth century."
http://www.bopsecrets.org/rexroth/communalism1.htm
If we mean "In what country would Marxist socialism be most likely to come to power?," most people in 1900 would say Germany. The SPD got 27.2 percent of the vote in the 1898 election
https://en.wikipedia.org/wiki/German_federal_election,_1898 and would get 31.7% in 1903.
https://en.wikipedia.org/wiki/German_federal_election,_1903 Officially the party was Marxist, and Bernstein's "revisionism" was condemned at party congresses.
https://books.google.com/books?id=yA8nBQAAQBAJ&pg=PT44 Kautsky was at this time much admired by Lenin, so it would be difficult to say that in 1900 one was a Communist and the other was not; indeed, even in 1920 Lenin referred admiringly to "Kautsky when he was a Marxist."
http://links.org.au/node/4186