Serbia was one of the countries fighting on the Allies side ( which included Russia, Great Britain and France.) Actually, the ww1 started when Austo-Hungary attacked Serbia. Then Russia, France and UK backed up the Serbs.
AUSTRIAHUNGARY
Germany was on the losing side of World War 1.
The side that lost world war 1 is central powers
japan
Britain's side
The allies
france
Turkey joined Germany in World War 1
on the allied side
Allies (british, French side)
Japan and Italy fought against Germany in World War 1 but were on Germany's side in World War 2
Italy