Complex sentence: In Poland, the cochineal trade was mostly monopolized by Jewish merchants who bought the dye from peasants in Red Ruthenia and other regions of Poland and Lithuania, and shipped it to major Polish cities such as Kraków, Gdańsk (Danzig) and Poznań.
Split into simpler sentences: In Poland, the cochineal trade was mostly monopolized by Jewish merchants, who bought the dye from peasants in Red Ruthenia and other regions of Poland and Lithuania. The merchants shipped the dye to major Polish cities such as Kraków, Gdańsk (Danzig) and Poznań.