Nations are just arbitrarily formed social groups in the meta sense, and concerning yourself with the well being of a 'nation' rather than individuals or simply the maximum number of people (globally or by citizenship) is a reactionary waste of time.
I grew up in an American irish & german catholic family. If I could obliterate my own families "national", cultural, and religious identity to replace it with one of overall human solidarity and rational sciences I would without hesitation. And I don't entirely trust anyone who wouldn't do the same for their own culture, no matter the sort.
Just because people within a nation are historically oppressed doesn't mean the nation itself is worth saving: the people within it need rights. They need material well being. They need education.
As a tool, using nationalism can have short term gains for leftwing movements, but often benefits nationalism more strongly in the long term, a rightwing ideology.
So why embrace such a short sighted and irrational thing bolted onto Marxism and Leninism? Why not just call yourself a Leninist?