The Great War began in 1914 and ended in 1918, the war was brought about by one little incident but by increasing tension among the nations of Europe, which included nationalism, imperialism, militarism and the Alliance system. A series of crises only hightened the tension between nations and when Archduke Ferdinand was assisnated; was was declared soon after.
Pride and strong feeling in one's nation was widespread at the beginning of the 20th century. Nationalist's believed that the needs of other nations were not as important as their own. Nationalist's were aggressive and were stubborn to forgive other nations when the felt their nation had been offended, this added tension among the nations of Europe.
Another long term cause was Imperialism. Imperialism was when a nation wanted to take over colonies and build an empire. The European nations had been taking over colonies since the 15th century and from 1870 there was fierce competition over which countires took over colonies over the world. Britain, Germany and France almost went to war over disagreements in North Africa. . Italy felt amnimosity towards France because they prevented Italy from setting up colonies. Many other countries went to war or almost came close to war because of the decreasing number of colonies. Imperialism caused tension among the nations because as each nation gained a colony, those colonies became dedicated to help their motherland in any event of war.
Militarism was the belief that one's country should be well armed and military ways could be used to gain nationalist needs. Militarists was an influential force throughout Europe. The Great Powers competed to build up their armed forces and supplies of weapons, thus this added to the escelating tension, fear and anger between the countries. .
There were many alliance agreements between the Great Powers before WW1 had broke out, and one alliance system became a long term cause of war because it divided Europe into two armed forces; Germany, Austria and Italy became allies and France, Russia and Britain joined forces.