There was the Triple Alliance aka the Central Powers. They had Germany, Austria-Hungary, Bulgaria, and the Ottoman Empire. The other guys, or the Allies, were the U.K., France, Russia, the U.S., and all of the European colonies in Africa. The Allies had allies like Portugal, Italy, Greece, Rumania, Serbia, and Libya too. The complex web of alliances was among the causes of WWI, as when one country attacked another, such as Germany to Poland, another country stood up for their friend, in Poland's case, their friend was Russia.