World War I (abbreviated WWI), or World War 1 or the First World War was a war fought in Europe between 1914 and 1918. Germany and England and France all fought over territory. This war was infamous for the first use of mustard gas and chemical warfare. It was also the first time that modern machine guns were used, which resulted in Bunker Hill type massacres of thousands during several offensives. The war ended up with the two armies facing each other in trenches where they stayed for years with no progress on either side. Artillery barrages erased some French towns from the map. The first tanks were used, as well as the first aerial combat (you know, Snoopy vs. The Red Baron). Everyone thought that the First World War was so terrible that no one would ever fight another war again. Silly humans!
Currently there are two Americans and one Briton alive who fought in World War One.
- The Austro Hungarian Empire declared war after their heir to the throne was assassinated by a Bosinian Serb in Sarajevo. 
- World War I was originally called the Great War, before World War II. This is because calling it the World War would have been silly, with the war only taking place in Europe.
- The Soviet Union started as a result of Russia getting smoked by the Central Powers in 1917. For exactly five years, the new communist nation was actually a good nation, because Vladimir Lenin and Leon Trotsky actually wanted to carry out the noble ideals of Karl Marx, apparently including the execution of innocent children, (The whole of the Tsar's family including children were murdered). Tragically, despite Lenin's objection, a crazy, evil, drunk named Joseph Stalin had Leon exiled after Lenin's death, and turned the Soviet Union and all of communism from a noble system dedicated to eliminating the tyrannical class-systems of capitalism, into an evil and oppressive organization that persecuted people who didn't agree with him.
- The part of the Middle East that is now Iraq also caused problems during World War I because the ships were changing from steam to diesel oil, and Iraq had the oil. When the Ottoman (Turkish)Empire decided to join the war Britain feared among factors the threat to oil supplies.
London immediately landed an Anglo-Indian force at Basra, near the estuary of the Euphrates and Tigris rivers. This was done to protect the Anglo-Persian oil pipeline, which was vital to the British navy 
Iraqi oil is always a mixed blessing for that country.