Bohemia was actually christianized by byzantian missionars in the 9th century. There never was a crusade there.rusades to Livonia or Bohemia,
Where did you get your history lessons? I am from Czech Republic. See hussite movement and crusade against it in the beginning of the fifteen century. But thats OOT (See Hussite wars on wiki)
Those others, thanks for tips.
As far as I checked all "Weather" demons are about waters, same as Gozreh. However as there is still Ice layer in Abyss I believe that Ruler of this Layer /to lazy to look after that now/ would like to cover the north under Ice.
Morever in my own group there will be Priestess of Winter (Slightly upgraded domains, Rules and Spells, from DnD 3.5 Frostburn). Especialy if I use the Slavs for Mendev, the concept of personalization of Winter will be strong. Same as other personalizations of seasons. There are no "Slav" gods in the world, even though there are strong concepts. I think the rebirth of Pulura through a new goddes, who would like to cover worldwound in purifing ice and frost will be one of the main stories. The Priestess of Winter should be Pulura Reborn!
Brevoy, Mendev, Irrisen all have strong slavic roots, however the natives are Ulfen /germans/ and Kellids /kelts/.
Irrisen is not interesting for me. The Mendev is place where people should be tested. Irrisen is Evil and it will be all agains devils. But in mendev there are a lot of lines you should follow. Begining with tensions between Native Ex-Iobaria tribes, Ulfen and Kellids natives, and crusadic upper class, taint of evil, real and invented heresy, faith and religion. Thats nice place for campaign. Same like Sargava, but in far different, and may be more harsh environment.