Lolworthy. If Nationalism is pushing for love of one's people, culture, heritage, and wanting a future for them, I see no reason why it would be incompatible with the notion of a King who is the father of that people.
Always remember, that the greatest king, God himself, despised Babel so much and so thoroughly that he had it destroyed, for he saw the existence of the different nations of the world (his creation) to be good and the attempt to unite them all to be degenerate and evil. And it was, for they were motivated in their vain,heretical attempt by the notion that would become like God. And that same notion is what has lead us to the hellscape before us now.
Do not stray from the path of the righteous.