By the way, for the Spanish army of those times you had Italian regiments, Spanish regiments and Walloon regiments and even German regiments
Wilst for most of them it's pritty clear (more or less) Walloon needs a little bit more of explanation, it just meant that the recruiting area for this regiment was in the area now called Belgium (more or less)that is also the Flemish speaking part. The regiments of Deynse (Deinze near Ghent), Westerlo (near Antwerp) and Grobbendonck (even nearer to Antwerp) were all labelled as Walloon regiments. Nothing to do with nowadays politics.