Which recent presidential candidate led one of the most successful independent campagins

Ross Perot was a presidential candidate in 1992, who lead one of the most successful independent campaigns.

Explanation:

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).