But it isn't, here. The state of Belgium created itself by secession from the United Kingdom of the Netherlands, and its populace generally comprises two nations, Flanders (Flemish) and Wallonia (French), neither of which are continguous with the state, nor particularly interested in sharing a national identity with each other.

In short, a state is about turf, and a nation is a people, and you need them both to look similar on a map to make a nation-state.