In case of what country's attack was the origins of the Central Powers?
Dual Alliance (1879) The Dual Alliance was a defensive alliance between Germany and Austria-Hungary, which was created by treaty on 7 October 1879 as part of Bismarck's system of alliances to prevent or limit war. The two powers promised each other support in case of attack by Russia. Also, each state promised benevolent neutrality to the other if one of them was attacked by another European power (generally taken to be France, even more so after the Franco-Russian Alliance of 1894). Germany’s Otto von Bismarck saw the alliance as a way to prevent the isolation of Germany and to preserve peace, as Russia would not wage war against both empires.
Russo-Turkish War (1877–1878) The Russo-Turkish War of 1877–78 (Turkish: "93 Harbi ('93 War)" ) was a conflict between the Ottoman Empire and the Eastern Orthodox coalition led by the Russian Empire and composed of Bulgaria, Romania, Serbia, and Montenegro. Fought in the Balkans and in the Caucasus, it originated in emerging 19th-century Balkan nationalism. Additional factors included Russian hopes of recovering territorial losses suffered during the Crimean War, re-establishing itself in the Black Sea and supporting the political movement attempting to free Balkan nations from the Ottoman Empire.