the prewar state of yugoslavia referred to its component regions as republics would a political geographer have called them states, nations, or provinces?

Nations

Explanation:

A nation is a group of people that have a cohesive culture: a common language, religion, customs, history. A nation can be a state (a nation-state) or not, and a state can include two or more nations (a multinational state). For example, Japan is a nation-state, but Russia is not.

The Yugoslavian republics were nations. The Slovenes for example are catholics, speak the Slovenian language, and identify themselves a central europeans. The Serbians are orthodox, speak the Serbian langauge, and identify themselves as Slavs, Balkans, and view Russia as an ally.