â€œGreat warâ€ is the other name of world war I. It was started due to many reasons but the foremost cause of all is the assassination of Archduke Frencis Ferdinand, the next heir of Austro-Hungarian Empire and his wife Sophie during their Serbia visit. They thought that if Ferdinand got the throne of Austro-Hungarian Empire then their sufferings and persecution would increase. Now Germany joined hands with Austria-Hungary and provoked them for the attack on Serbia and the war was started on June 28, 1914. Russia joined the other side i.e. the Serbians. Germany now declared war on Russia and France as well. So Russia, France, Britain signed a treaty known as triple entente and helped the Serbia. Two groups were formed one was the triple entente i.e. Russia, France, Britain and other triple alliance of Austria, Germany and Italy. As half of the world was under British rule so automatically those countries that were under their rule also got involved which led to World War I.
Another reason which came up was nationalism that was growing at very fast pace in Europe. People in Europe of common culture and language wanted to have their own separate country. This was the main threat for Austro- Hungarians as they wanted stability in their power.
Militarism also contributed for world war I. England wanted to have more and more power i.e. arms and navy as compared to Germany so that they can keep away their enemies. They built lot warships in competition with Germany.
So we can say that including assassination of Archduke Ferdinand, nationalism and militarism, imperialism and system alliance also contributed towards the World War I.