I'd have to re-read Stalin's 'Marxism and the National Question' again, but I think in a more or less simple take; The Socdems of the Colonized world and of the Imperial Periphery are fighting for their country's right to nationally self-determine, whereas the Succdems of the Imperialist nations of the inner and outer core have no urge to fight for national self-determination as their countries stand at the apex. The Imperial succdems fight to preserve what is taken whereas the Colonial socdems fight to retrieve what is stolen.