The immediate spark that instigated World War I was the assassination of Archduke Franz Ferdinand and his wife. Ferdinand was the heir to the throne of the Austro-Hungarian Empire. The assassination took place at Sarajevo in June, 1914. Other factors allowed this spark to lead to world war. One of these factors was imperialism. Imperialism allowed countries to increase their power and wealth by taking control of other countries. The desire to establish even greater empires led to increased competition and confrontation among countries. As a result, some countries spent huge amounts of money to build up very powerful militaries. They also formed alliances to help maintain their economic and political dominance.
The first alliance to be formed was comprised of Germany, Austria-Hungary and Italy. Then Russia, England and France formed an alliance and when the United States joined that alliance, it truly became a world war.