Poland will be one of playable nation in mod?
I can write few interesting facts about Polish history and if you have any question about it I can asnwer it. Listining (or rather reading :)) to me:
I do believe they did have black powder.
In 1241 near Legnica (city in Silesia) troops of Polish duke of Silesia, Henryk II Pobożny (Henry II Devout) lost with invaders from far east - Mongols. One of reasons why he lost battle (life too) is that Mongols used weapons based on black powder or military gases - in result part of Henry's army run away.
And Greek fire! That was the flame-thrower I meant. I think i read there was a mention of grenades.
Greek fire not only in Byzantine Empire but in Arabic states and China. About "granades":
there are few photos from museum (10th -12th c).
I don't know who invented cannons but I can write few facts:
Teutonic Order used cannons when they besieged Kowno (city in Lithuania) in 1362. In 1410 battle near Grunwald, Teutonic Order used against Władysław II Jagiełło troops (I don't remember number of cannons). In 1383 during besieging Pyzdry, Polish forces used cannons.
In Poland many thing came 25-50 years after it appeared in West Europe. Thinking this way first cannons in Europe should appeared in first half of XIVth century. In which countries? I suppose it should be Italy, Spain, France or Holy Empire. I will try to find more informations in books, ok?