"People" tout court may do in this context but Staatsvolk has variously been translated as constitutive people, state people (by Hobsbawm among others), national people, and ethnic people. All of these options sound a bit clumsy in English but they are arguably justified to distinguish them from "people." I'd write something like, "In 1949, Tibet, which was recognized as a sovereign state under international law and which had its own constitutive people, territory, and currency, was annexed by the PRC; it has been devastated under its rule since then."