Dutchies being rebellious as always ;) image - West Slavic Kinship: Heart of Europe mod for Europa Universalis IV

This mod introduces lots of changes ranging from the Netherlands to Poland and from Denmark to Italy. Many new provinces, cultures, historical countries for the 1444 start and formable or releasable nations (both historical and hypothetical), while staying mostly true to the original vanilla mechanics and the overall game balance, so you don't need to re-learn how to play the game as is the case with some of the overhaul mods.