The origins of World War One, also known as "The Great War", can be traced back to three specific details - the European Alliance system, the growing distrust between various European powers, and the act of an assassin.
The complex system of European alliances meant that even the smallest confrontation could easily escalate into a "Great War" involving most of the countries of Europe, and a significant number of international countries, including Australia.
This is exactly what occurred at the beginning of World War One - Germany was allied to Austria-Hungary, whom were also allied to Italy. Serbia was protected by Russia, who was in turn allied to France. Britain was "morally obliged" to protect France, and also had a treaty to protect Belgium. Britain also had a firm control over the nations of its Commonwealth - Australia, Canada, The South African Republic, India, and New Zealand. Many other countries including, ironically, Italy, also joined the fight against Germany and Austria-Hungary, to gain appreciation from the internationally powerful Allies.
The growing power and competition between these large European states created a tinderbox continent - the spark appeared in 1914. The countries of Germany, Britain, France, Russia and Italy were perhaps the most powerful countries of the time - and as such were ever more greedy for increased power in Europe. The period of World War One also saw great technological change both Socially and Militarily - most of the nations of WWI had become industrialised, with industrialised armies also. The European Generals were most likely eager to try out their new weaponry, yet unaware of its potential impact across the world. The growing Diplomatic uneasiness is also showcased in the film, "Breaker Morant" - British soldiers were eager not to harm German citizens in fear of a potential backlash from Germany. .
The spark that ignited this tinderbox of Alliances and armies was a seemingly-mundane act from a political terrorist group, the "Black hand".