Reject competitive, nationalist projects in all their forms. Enterprise instead to build on solidarity. There is no negotiation that will ever yield egalitarian results like collaboration, between people of common interests and sane priorities. This pattern itself must compete with nationalism, but it will win, because solidarity for socialists is not simply a commitment to material bonds. It is transcendant of nations without any loss of their full content or character. A synthesis.
A growing, now media-adopted neoliberal, ethnonationalist conception of progressive identity politics threatens those prospects today, and I see it gripping many leftists otherwise committed to real systems change. I wish I could articulate this better, but every application is fraught and I'm trying to focus on a pattern here. We have some self-critique to do as a left movement of our ability to place ourselves within it, and among others, and learning what it really means to include everyone.