World War I was an International conflict that in 1914–18 involved most of the nations of Europe along with Russia, the United States, the Middle East, and other regions. Some of the causes for the First World War were imperialism, militarism, and nationalism. The war became so large was because of the alliances. If one was involved, all were involved. There were countries that only fought because of their commitment to another. The Allies included the British Empire, France, Belgium, Russia and later, the USA. The Central Powers of Germany, Austria Hungary, Bulgaria and Turkey were a part of the other alliance group.
One cause was imperialism. A country increases their power and wealth by bringing additional territories under their control. Before World War I, Africa and parts of Asia were points of contention among the European countries. Because of the raw materials these areas could provide, tensions around these areas ran high. The increasing competition and desire for greater empires led to an increase in confrontation that helped push the world into World War I. Each country wanted to be the best and was willing to do anything for it.
Another cause of the First War was militarism. As the world entered the 20th century, an arms race had begun. By 1914, Germany had the greatest increase in military buildup. New weapons were coming in play, which brought a new level of power to the military. Great Britain and Germany both greatly increased their navies in this time period. Further, in Germany and Russia the military establishment began to have a greater influence on public policy. This increase in militarism helped push the countries involved into war.
A Third main cause of this historical event was nationalism.