Who was involved in WWI?

The First World War involved many of the world's great economic powers unified into two opposing forces- the Allies Powers and the Central Powers.

The Allied Powers grew out of the Entente Alliance of 1907 and the primary nations were the French Republic, the British Empire, and the Russian Empire. Other countries which supported and made up the Allied Powers include Armenia, Belgium, Greece, Hejaz, Japan, Poland, Portugal, Romania, Serb-Croat-Slovene, and Czechoslovakia. Initially, Italy sided...

The First World War involved many of the world's great economic powers unified into two opposing forces- the Allies Powers and the Central Powers.

The Allied Powers grew out of the Entente Alliance of 1907 and the primary nations were the French Republic, the British Empire, and the Russian Empire. Other countries which supported and made up the Allied Powers include Armenia, Belgium, Greece, Hejaz, Japan, Poland, Portugal, Romania, Serb-Croat-Slovene, and Czechoslovakia. Initially, Italy sided with the opposing Central Powers, but in 1915 sided with the Allied Powers.

The Central Powers were initially comprised of Germany and Austro-Hungary, but they were later joined by the Ottoman Empire and Bulgaria. 

In 1917, the United States declared war on the Central Powers, though were not considered part of the Allied Powers.

Keep in mind that at this time, Empires and nationality stretched far beyond the borders of what we today consider to be Turkey, France, or Great Britain. Much of Africa was controlled by one European nation or another at this time, and so can be said to have been involved in World War One indirectly.