Hypothetically;
Justify this scenario.
In your country, you have easy access to life saving technologies and medicines. They are ubiquitous, and the costs of making them available overseas is minimal. However, it is not in your nation's interest to do so, because political reasons.
Nationalism always boils down to exactly that kind of situation. It could be availability of iron. Copper. Oil. Whatever. Something that your country has in abundance, that another does not, and suffers from that lack of abundance over. There is implicit justification that the refusal to make those resources available to another country's populace, at anything other than a one-sided deal, is simply unthinkable.
Why is that?
My basic answer: US vs THEM. We justify it on the terms that those are OUR resources, and that if THEY want access to them, then they need to give US something of slightly greater value, to justify our losing access to those resources. (Meanwhile, we have no problems at all shipping those resources, often at great expense, all around our own country to maximize local national utility of that resource.)
EG-- Denying a 3rd world country of life saving medicine, because "They have to be profitable to us! We cant just GIVE stuff away! That's UNTHINKABLE! We gotta look out for $"Nationality" interest!!", is defacto "Abusing other countries".
Specifically, we are abusing their position (as relates to that resource availability) to extract concessions from them. This is functionally equivalent to extortion-- The implicit threat, is that they will have to accept a diminished quality of life (imposed by our refusal to share that essential resource with them), if they do not meet OUR demands.
"That's a nice populace you have there-- It would sure be a shame if some highly infectious but easily treated disease started killing them because you lack the means to treat it yourselves. *nudge nudge*"
etc.