Nationalism actually: The people and products and culture from this country are better than those from another country because they are from this country.
Interesting how many different (not so charitable) interpretation of this comic exist in thr comments.
To me this of course a simplification, as its a comic and was postes in !memes
In my opinion this comic shows how nationalism can be used to pit the working class against each other even tho their class interests are pretty similar, no matter which side of the border they are.