Nationalism and socialism as actually lived and applied in the 20th century are the same thing (and in the 18th and 19th century, nationalism was often a force for classical liberalism!). It’s all a kind of reactionary tribalism (another “ism” which becomes poisonous quickly as you up the dosage). When you nationalize an industry, you socialize it. When you socialize an industry you nationalize it. Yes, international socialism rejected this formulation. And that’s why international socialism failed! People wanted to be Germans or Russians or Italians, and they wanted to be socialists. Even the Soviet Union embraced national-socialism (socialism in one country) because that 'workers of the world unite' crap wouldn't fly. After Stalin, no Communist or socialist regime failed to exploit nationalism to one extent or another.