An ethnic group or ethnicity is a category of people who identify with each other based on similarities such as common ancestral, language, social, cultural or national experiences.... Membership of an ethnic group tends to be defined by a shared cultural heritage, ancestry, origin myth, history, homeland, language or dialect, symbolic systems such as religion, mythology and ritual, cuisine, dressing style, art, and physical appearance.
you cóuld ve used frisians. If im not mistaken the country once was divived into frisians saxons and francs, though noone nowadays identifies with the latter too.
Though there is a real distinction between the people from the south of the country and the west or north.