I really believe this, and this is the impression I get from my historical reading.
The problem is that I don't have much of a head for history, so I can rarely marshal my scattered impressions when I get into an argument.
But today I was reading about St. Hedwig, a Queen of Poland in the fourteenth century. Her father had intended another one of his daughters for the throne, and arranged a marriage with a foreign king, but the Polish nobles weren't pleased about it.
Wikipedia says: "However, both her daughters had been engaged to foreign princes (Sigismund and William, respectively) unpopular in Poland. Polish lords who were opposed to a foreign monarch regarded the members of the Piast dynasty as possible candidates to the Polish throne."
What's this? That sounds very nationalistic. Way back in the fourteenth century. But wasn't nationalism invented in the nineteenth century? The neo-reactionaries who are all about aristocracy and disdain nationalism wouldn't approve.
And I've encountered hundreds of similar little references in my historical reading through the years. Maybe I should compile a dossier.