Answer:
Serbia
Explanation:
Austria-Hungary declares war on Serbia. On July 28, 1914, one month to the day after Archduke Franz Ferdinand of Austria and his wife were killed by a Serbian nationalist in Sarajevo, Austria-Hungary declares war on Serbia, effectively beginning the First World War
Invasions by Barbarian tribes
Economic troubles and overreliance on slave labor
It protected the sultan's power by providing him with a group of extremely loyal officials and soldiers is why the Devshirme system was so important to the Ottoman Empire. The correct option among all the options that are given in the question is the fourth option or option "D". I hope the answer comes to your help.