The Crown of Poland was a constitutive state of the Polish-Lithuanian Commonwealth. However, when the Dual Commonwealth felt apart in early 20th century, at the Peace Conferences at Frankfurt it was decided to divide the territory in four states. First among the traditional divisions between the Crown (Poland) and the Grand Duchy of Lithuania, and then the former Crown territories were divided between Poland and Ruthenia with an approximate division between East and West Slavic ethnicities (whatever people at Frankfurt thought that would meant).
Poland has been, politically, the most stable nation of the former Dual Commonwealth, and is a founder member of the Baltic Common Market.
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