I don’t remember Marx ever espousing a singular imminent world revolution, or that the state will wither away under current conditions, or that class will override nationalism. If he did, then indeed he was wrong about those subjects.

Nevertheless there were socialist revolutions all across the world that encompassed a good chunk of the planet for a time; and in many countries that didn’t end up becoming socialist, there were revolutionary conditions that weren’t turned into a changing of class relations due to lack of a proper vanguard party because socialism isn’t that automatic and deterministic. Even if it doesn’t look like it right now, all of the world will eventually be encompassed by socialism; reactionaries don’t see round two coming, but it will, mark my words.