The answer is Russia. The Central Powers (also known as Quadruple Alliance) consist of Germany, Austro-Hugarian Empire, Bulgaria and the Ottoman Empire. German Empire and Austro-Hungarian Empire were the two original members of the Central Powers. The Ottoman Empire joined around 1914 while the Kingdom of Bulgaria joined the following year. The Central powers was one of the two main faction of the war. They were defeated by the Allied Powers .The name Central Powers derived from the geographic location f these countries.
