An ethnically and linguistically mixed historical region in modern day southwestern Poland, bordering the Czech Republic (and some of its southern parts even being a part of the northeastern Czech Republic).
In Petike's Sparrow Avengers Universe, Silesia became an independent country again after the First World War. It then existed under several vastly different political regimes until the late 1940s. A few years after the end of the setting's alternate World War Two, Silesia became a member state of the Confederation of Polish Peoples. In the 50s, as a state of the Confederation, it also became a founding member of the Visegrad Union, a political union of Central European countries.