Maybe its a false dichotomy. I believe in “globalism” to an extent, its just that in the form _I_ believe in, we put America and Americans first. I believe a stronger and more prosperous America benefits the entire world.
Like most arguments, the problem is mostly in the definitions.
If globalism means exchanges of goods services and even people among all the world’s countries based on rules decided by each country, then there is no inconsistency between nationalism and globalism. That’s been the world order since the treaty of Westphalia.
If globalism instead means one world central government then the very concept of nationhood and national self determination disappears.
We as humans have not reached the point where we can set up a single optimal government that works best for everyone. So nations, like states in the US, serve as “government laboratories” where different approaches are tried, and thus slowly evolving to better governments.
I can’t think of anything worse than setting a central world government at our stage of human development.