The political structure of the roman empire included all of the following from the roman republic except
a senate
checks and balances
plebeians and patricians
imperial provinces

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).