World War I World War I was the first major war that included a country from almost every part of the world. It was the second bloodiest war second only to W.W.II. The greatest destruction that humankind had ever previously experienced began on a calm and beautiful August day. It was a senseless slaughter that no nation benefited from. It lasted from 1914-1918. America was involved from April of 1917 to November of 1918. It ended with the Treaty of Versailles, which was signed on November 11 at 11:11 a.m. in 1918. World War I started because of the assassination of Franz Josef Ferdinan and his wife Sophie while they were in a motorcade in the capitol city of Bosnia an