 Complete the following phrase:  Various economic and military policies instituted by Andronikos II, such as the reduction of military forces, weakened the empire and left it vulnerable to attack. In the mid-14th-century, the Ottoman Turks began a strategy of gradually taking smaller towns and cities, cutting off Constantinoples supply routes and strangling it slowly. On 29 May 1453, after an eight-week siege during which the last Roman emperor, Constantine XI, was killed, Sultan Mehmed II the Conqueror 