Question: What is the name of this unofficial, historical designation for the German state, in which the Frontier March of Posen-West was a province of the Free State of Prussia?
Sentence (from "Posen-West Prussia"): The Frontier March of Posen-West Prussia (German: "Grenzmark Posen-Westpreußen" , Polish: "Marchia Graniczna Poznańsko-Zachodniopruska" ) was a province of the Free State of Prussia within the German Weimar Republic.
Relevant evidence: Yes