Answer: Germany, Austria-Hungary, Bulgaria, and the Ottoman Empire
Context/explanation:
In the years prior to World War I, there was much military buildup and alliance formation happening among the nations of Europe. This all served to increase tensions between the nations of Europe. There was pressure to form alliances with other nations to strengthen a nation's defenses in case there was a war. The Triple Entente and the Triple Alliance set up in opposition to each other. The Triple Entente consisted of Britain, France and Russia. The Triple Alliance consisted of Germany, Austria-Hungary, and Italy. When the war broke out, Italy shifted its loyalties and sided with the Allies (Britain, France, Russia). Germany and Austria-Hungary picked up Bulgaria and the Ottoman Empire as additional allies during the war, known as the Central Powers.