Question: In case of what country's attack was the origins of the Central Powers?

Context paragraphs:
Naval warfare of World War I: Naval Warfare in World War I was mainly characterized by the efforts of the Allied Powers, with their larger fleets and surrounding position, to blockade the Central Powers by sea, and the efforts of the Central Powers to break that blockade or to establish an effective blockade of the United Kingdom and France with submarines and raiders.

Central Powers: The Central Powers (German: "Mittelmächte" ; Hungarian: "Központi hatalmak" ; Turkish: "İttifak Devletleri" or "Bağlaşma Devletleri" ; Bulgarian: Централни сили "Tsentralni sili" ), consisting of Germany, Austria-Hungary , the Ottoman Empire and Bulgaria – hence also known as the Quadruple Alliance (German: "Vierbund" ) – was one of the two main factions during World War I (1914–18).  It faced and was defeated by the Allied Powers that had formed around the Triple Entente.  The Powers' origin was the alliance of Germany and Austria-Hungary in 1879.  The Ottoman Empire and Bulgaria did not join until after World War I had begun, although the Ottoman Empire retained close relations with both Germany and Austria-Hungary since the beginning of the 20th century.

Siege of Medina: Medina, an Islamic holy city in Arabia, underwent a long siege during World War I.  Medina was at the time part of the Ottoman Empire.  In the war, the Ottoman Empire sided with the Central Powers.  Sharif Hussain of Mecca revolted against the caliph and the Ottoman Empire which, under the leadership of the nationalistic Young Turks, had ignored the wishes of the Caliph and sided with the Central Powers.  Hussain instead sided with the British Empire.  T. E. Lawrence was instrumental in this revolt.  Hussain occupied Mecca and besieged Medina.  It was one of the longest sieges in history that lasted till even after the end of war.  Fahreddin Pasha was the defender of Medina.  Some celebrated him as ""the Lion of the Desert"" despite the suffering of those who remained in Medina.  The siege lasted two years and seven months.

Leaders of the Central Powers of World War I: The leaders of the Central Powers of World War I were the political or military figures who commanded or supported the Central Powers during World War I.

Ilie Bărbulescu (linguist): Ilie Bărbulescu (December 3, 1873 – June 5, 1945) was a Romanian linguist and philologist who specialized in the Slavic languages, also noted as a political journalist and Conservative Party cadre.  Academically trained in his native country and in the Kingdom of Croatia-Slavonia, he investigated in particular the Slavic influence on Romanian and the origins of Romanian literature, with additional interests in Old East Slavic and Russian literature.  He was a corresponding member of the Romanian and Serbian Academies, and helped establish a Slavic studies department at the University of Iași.  Bărbulescu was nevertheless a controversial figure, deeply involved in academic rivalries, and taking up unpopular political stances—especially during World War I, when, contrary to his background in Slavistics, he took up "Germanophilia", rooting for the Central Powers.

Flămânda Offensive: The Flămânda Offensive (or Flămânda Maneuver), which took place during World War I between 29September and 5October 1916, was an offensive across the Danube mounted by the Romanian 2nd Army supported by Romanian coastal artillery.  Named after the hamlet of Flămânda, the battle represented a consistent effort by the Romanian Army to stop the Central Powers' southern offensive led by August von Mackensen.  The battle ended as a tactical victory for the Central Powers.

Second Battle of Cobadin: The Second Battle of Cobadin was a battle fought from 19 to 25 October 1916 between the Central Powers, chiefly the Bulgarian Third Army and the Entente, represented by the Russo - Romanian Army of the Dobrogea.  The battle ended in decisive victory for the Central Powers and the occupation of the strategic port of Constanţa and capture of the railway between that city and Cernavodă.

Niedermayer–Hentig Expedition: The Niedermayer–Hentig Expedition was a diplomatic mission to Afghanistan sent by the Central Powers in 1915–1916.  The purpose was to encourage Afghanistan to declare full independence from the British Empire, enter World War I on the side of the Central Powers, and attack British India.  The expedition was part of the Hindu–German Conspiracy, a series of Indo-German efforts to provoke a nationalist revolution in India.  Nominally headed by the exiled Indian prince Raja Mahendra Pratap, the expedition was a joint operation of Germany and Turkey and was led by the German Army officers Oskar Niedermayer and Werner Otto von Hentig.  Other participants included members of an Indian nationalist organisation called the Berlin Committee, including Maulavi Barkatullah and Chempakaraman Pillai, while the Turks were represented by Kazim Bey, a close confidante of Enver Pasha.

Treaty of Brest-Litovsk (Ukraine–Central Powers): The Treaty of Brest-Litovsk was a peace treaty signed on March 3, 1918 between the Russian SFSR and the Central Powers, but prior to that on February 9, 1918, the Central Powers signed an exclusive protectorate treaty (German: "Brotfrieden" , "peace for bread") with the Ukrainian People's Republic as part of the negotiations that took place in Brest-Litovsk, Grodno Governorate (now Brest, Belarus) recognizing the sovereignty of the Ukrainian republic.  Although not formally annexing the territory of the former Russian Empire, Germany and Austria-Hungary secured food-supply support in return for providing military protection.  The Quadruple Alliance recognized Ukraine as a neutral state.

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.

Supporting paragraphs: Central Powers Dual Alliance (1879)
Answer: Russia