Russia supported Serbia first, then when Germany entered the war (on the side of Austria-Hungary--the Central Powers), France and Britain joined in as well (on the side of Serbia--The Allies). Bulgaria joined in later (Central Powers), as did Italy (Allies). As it became truly a world war, Japan and the United States joined (part of the Allies), and so did the Ottoman Empire (Central Powers), and several other countries such as Portugal, Romania, etc. on the Allied side.
some countries supported Austria-Hungary (like Germany...) and some supported Serbia (like Russia...) and then World War I started...
some countries supported Austria-Hungary (like Germany...) and some supported Serbia (like Russia...) and then World War I started...
Germany was the first country to declare war on Serbia in World War 1. The other countries were pulled into the war because the had alliances with either Serbia or Germany.
Montenegro and Serbia
The countries that started World War I were Serbia, Austria-Hungary, Germany, and Russia. Those were the base and then more countries joined.
Austria-Hungary and Serbia.
England
United States supported South Korea after World War 2.
United States supported South Korea after World War 2.
United States supported South Korea after World War 2.
United States supported South Korea after World War 2.
WW1 actually started as a conflict between the small country of Serbia and Austria-Hungary because Serbia supported the assasination of the Archduke or Austria-Hungary. Because Serbia was in an alliance with Britain, it had an obligation to enter the war, along with many other countries that entered on both sides of the intricate system of alliances that made up Europe and caused World War 1.