Answer: The underlying cause behind the First World War was the simmering suspicion and hostility among various European powers due to historical and concurrent factors precipitated by imperial drives. The immediate trigger for the first world war was the assassination of the Archduke Franz Ferdinand, heir to the Austro-Hungarian throne. Factors behind the first world war:

• Crisis preceding the World War: Moroccan crisis (1905-06) where Italy, Spain, Russia and Britain supported France and later got control over Moroccan Banks and Police, was a diplomatic defeat for Germany.
  • Similarly, the Bosnia Crisis of 1908 wherein Austria-Hungary annexed Bosnia from the weak Ottoman empire, which led to the humiliation of Russia that began its militarization.
  • Balkan wars 1 and 2 of 1912 and 1913 further fueled the crisis.
• The alliance systems: The Triple Alliance involving Italy, Germany, and Austria and the Dual Alliance between France and Russia, which with inclusion of England became the Entente Cordiale, caused the split of Europe into two rival camps.
• Militarism and arms race: Starting with France, the countries of Europe developed a system of maintaining large armies and navies and engaged in arms race in the name of self-defence. It created fear and suspicion among the nations, especially between the British and the Germans.
• Colonial rivalry in Africa and the Far East: The countries of Europe competed with each for market access and new sources of raw materials. This led to the scramble for Africa and competition in the Asian countries such as India, China, and Malay regions. Countries which were left behind in this race, such as Germany, Italy, and Japan, aggressively pursued colonial imperial policies to secure and advance their interests.
• Nationalism: The whole of Europe was swept under a wave of nationalism that affected the relations between France and the UK; France and Russia; Germany and France & UK, the Habsburg empire and Serbia. All these countries tried to safeguard themselves by resorting to alliances, preventive wars, and militarism.

Also, there was a cultural belief amongst these imperialist nations that war was good, necessary, glorious and it established the notion of superiority. The First World War lasted more than four years between 1914 and 1919 and between 15 and 19 million people around the planet were killed. Also, the War devastated the global economy and contributed to massive disease outbreaks that killed millions more.