This, and Czechoslovakia too, down to the point of using the same "pan-slav" color scheme, and even having variations of the same pan-slavic song as their national anthems - Hej, Slovane! If you read early 20th century left-wing literature, like Hasek's The Good Soldier Svejk, pan-slavism, stated or not, definitely played a revolutionary role especially in Slavic lands under imperial occupation. You have music like the Glagolitic Mass, which despite being written by secular composer from a largely Catholic culture, paid tribute to a joint Slavic history.
I think the term pan-slavism refers to the secular, left-leaning version of slavic trans-national solidarity, and usually, the Czarist Great Russian chauvinist version of it is dubbed "Slavophilia" in most sources I've read.
My general opinion as a non-slav is that Slavs, regardless of their geographic clustering, are more similar to one another culturally and even economically than any other European ethno-linguistic group, and while I wouldn't encourage them to make a geographic corridor through my country, I think they probably would be better off in some supra-national federation rather than (no pun intended) balkanized as they currently are. I definitely think Yugoslavia and Czechoslovakia were great countries and preferable to the current setup, and see them more as failures of joint identity building rather than state building; to my mind there's hardly any difference between a Czech and a Slovak or a Serb and a Croat and see no reason why these regional identities had to be maintained as they were rather than jointly assimilated.