Who was involved in the First World War? Who was on each side?

Which countries were in the two big alliance blocs: the Triple Alliance and the Triple Entente, before WW1? As part of our 'History Extra explains' series, leading historians answer the burning questions you were too afraid to ask...

A colour illustration of First World War allies, the German Reich and Austria-Hungary, featuring soldiers shaking hands, their troops and national flags, c1915. (Photo by Popperfoto/Getty Images)

Before 1914 the Great Powers were in two big alliance blocs: the Triple Alliance (Germany, Austria-Hungary and Italy) and the Triple Entente (France, Russia and Britain).

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British troops go over the top of the trenches during the Battle of the Somme, 1916. The Somme was one of the bloodiest clashes of the First World War, causing more than one million casualties over five months. (Photo by Paul Popper/Popperfoto/Getty Images)

The war extended and changed these two sides. Germany and its allies were known as the Central Powers: Germany and Austria-Hungary, later joined by the Ottoman Empire (Turkey plus the Middle East) and Bulgaria. The war quickly involved countries not part of the Triple Entente, so the opposing side was known as the Allies: Serbia, Russia, France and its Empire, Belgium, Montenegro and Britain and its Empire, including self-governing colonies like Canada and Australia.

Italy changed sides and joined the Allies in 1915. Other Allied nations included Portugal, Japan, Greece, Romania, China and, towards the end of the war, various South American countries, including Brazil and Peru.

The United States fought alongside the Allies from 1917, but as an ‘Associated Power’ with no formal military alliance.

Seán Lang is a senior lecturer in history at Anglia Ruskin University, and the author of First World War for Dummies.

For more burning historical Q&As on the Tudors, ancient Rome, the First World War and ancient Egypt, click here.

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This answer was first published by History Extra in January 2016