Ok, some ideas: told which one are well-suited to CK and I will provide more details.
Invasion of Mongols (there were how many, three or four of them?) On of them destroyed first attempt to reunite Poland, and another one devastated Lesser Poland.
German colonisation: A lot of settlers from western Europe was arriving into Poland, invited by Piast princes. That increased wealth and knowledge, but created a lot of tensions, which resulted in open ethnic animosities in XIV century (e.g. uprising in Cracovia and slaughter of everyone who was unable to repeat "ko³o, miele, m³yn")
Silver in Silesia - Silver rush which caused fast economical development of the country, invited a lot of miners and fortune seekers from everywhere. Piast pricnes of Silesia were really rich because of that. And they were then looking for silver anywhere in Poland, mostly without such success as in Silesia. Some Gold and silver can still be found in Silesia, and definetely you still can find mysterious signs left but Miners (how they were called, Walons??)
Black plague - it omitted Poland, mainly because of strict quarantine introduced by Kazimierz the Great.
Tolerancy for Jews - Jews were in Poland since XI century, and were granted privileges later. They were again encouraged to came here, especially later by Kazimierz the Great, to bring wealth and knowledge.
Struggles between archbishops of Magdeburg over the bishopry of Posen (poznan). Magdeburg thought Poznan should belong to its dioecese, while Gnesen, supported by Polish dukes, thought exactly the opposite.
The "St. Peter" tax which meant additional burden on peasants, nobles etc.
Pagans were still active in XI century. in 1066 it's just generation or two after last great pagan uprising which smashed every church, noble etc.
Colonisation of Prussian lands and tensions with Prussians - raids and counterraids...
Of course Poland, due to dynastic ties, will be heavily involved in the affairs of Rusin princedoms...
Invasion of Mongols (there were how many, three or four of them?) On of them destroyed first attempt to reunite Poland, and another one devastated Lesser Poland.
German colonisation: A lot of settlers from western Europe was arriving into Poland, invited by Piast princes. That increased wealth and knowledge, but created a lot of tensions, which resulted in open ethnic animosities in XIV century (e.g. uprising in Cracovia and slaughter of everyone who was unable to repeat "ko³o, miele, m³yn")
Silver in Silesia - Silver rush which caused fast economical development of the country, invited a lot of miners and fortune seekers from everywhere. Piast pricnes of Silesia were really rich because of that. And they were then looking for silver anywhere in Poland, mostly without such success as in Silesia. Some Gold and silver can still be found in Silesia, and definetely you still can find mysterious signs left but Miners (how they were called, Walons??)
Black plague - it omitted Poland, mainly because of strict quarantine introduced by Kazimierz the Great.
Tolerancy for Jews - Jews were in Poland since XI century, and were granted privileges later. They were again encouraged to came here, especially later by Kazimierz the Great, to bring wealth and knowledge.
Struggles between archbishops of Magdeburg over the bishopry of Posen (poznan). Magdeburg thought Poznan should belong to its dioecese, while Gnesen, supported by Polish dukes, thought exactly the opposite.
The "St. Peter" tax which meant additional burden on peasants, nobles etc.
Pagans were still active in XI century. in 1066 it's just generation or two after last great pagan uprising which smashed every church, noble etc.
Colonisation of Prussian lands and tensions with Prussians - raids and counterraids...
Of course Poland, due to dynastic ties, will be heavily involved in the affairs of Rusin princedoms...