 Michael's successors ruled the Byzantine Empire at its weakest point in history, and much of the Palaiologan period was a time of political and economical decline, partly due to external enemies such as the Bulgarians, Serbs and Ottoman Turks, and partly due to frequent civil wars between members of the Palaiologos family.By the beginning of the 15th century, the emperors had lost any real power, with the empire effectively having become a client state to the new Ottoman Empire.Their rule of the empire continued until 1453, when Ottoman sultan Mehmed the Conqueror conquered Constantinople and the final Palaiologan emperor, Constantine XI Palaiologos, died in the city's defense.