How did it get started? -Mutual Defense Alliances-Over time, countries throughout Europe made mutual defense agreements that would pull them into battle. These treaties meant that if one country was attacked, allied countries were bound to defend them.
Imperialism -is when 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. This was especially true because of the raw materials these areas could provide. The increasing competition and desire for greater empires led to an increase in confrontation that helped push the world into World War I.
Militarism -As the world entered the 20th century, an arms race had begun. By 1914, Germany had the greatest increase in military buildup. Great Britain and Germany both greatly increased their navies in this time period. Further, in Germany and Russia particularly, the military establishment began to have a greater influence on public policy. This increase in militarism helped push the countries involved into war.
Nationalism -Much of the origin of the war was based on the desire of the Slavic peoples in Bosnia and Herzegovina to no longer be part of Austria Hungary but instead be part of Serbia. In this way, nationalism led directly to the War. But in a more general way, the nationalism of the various countries throughout Europe contributed not only to the beginning but the extension of the war in Europe. Each country tried to prove their dominance and power.
Immediate Cause: Assassination of Archduke Franz Ferdinand -The immediate cause of World War I that made the aforementioned items come into play (alliances, imperialism, militarism, nationalism) was the assassination of Archduke Franz Ferdinand of Austria-Hungary