Answer:
Allied Powers were Britain, France, Russia, Romania, Serbia, Belgium, Montenegro, Greece, Portugal.
Central Powers were Germany and Austria Hungary, who were later supported by Bulgaria and Ottoman Empire.
Italy was a member of Central Powers, but after the treaty of London in 1915 changed sides, and supported the Allies.
Step-by-step explanation:
War began on July 28, 1914 when Austria Hungary declared war on Serbia. Many countries interfered and supported one or other side.
Allied Powers had more support not only in Europe, but even some countries on the other continents supported its causes.