Most historians believe World War I was the product of Trans-European increases in militarism, imperialism, nationalism, and alliances made in the hundred years leading up to the war. The catalyst directly responsible for triggering the war was Franz Ferdinand’s assassination by Gabrilo Princip. In response to his death, Austria-Hungary laid out an impossible ultimatum for Serbia, the country where Ferdinand died and after a few days declared war. Ferdinand was not very popular with the Austro-Hungarian government and his death served only an excuse for the government to carry out its imperialist plans while flexing its newly strengthened military. The increased nationalism across Europe led to huge support for war across all nations. The scale of the war, and by extension, the body count also increased because of the alliances forcing many nations to participate. By declaring war on Serbia, Austria-Hungary dragged Germany, Italy and Russia into the war. Germany took this in stride, seeing an opportunity to expand into Belgium to get to France. Britain recognized this as a violation of the Treaty of London and when the Germans refused to stand down the British entered the war that would claim more British men’s lives than World War II.Keep looking, there’s more: Causes and Consequences of the First and Second World Wars