Wich book, written by baldassare castiglione, describes how nobles should behave at a royal court?

The book of courtier. :)

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).

the properties of a free-market system that determine what the out comes will be.