WWI was essentially the byproduct of European imperialism and entrenched ethnic conflicts. As countries rushed to increase their land holdings in order to increase their empires, they came into conflict with one another. The more colonies and land holdings that the countries had, the more they felt compelled to build their military forces to protect them. In order to ensure their interests, countries made alliances and counter alliances, stoking the fires of enmity.
Click on the image and explore the causes of WWI
The start of WWI has frequently been attributed to the assassination of Franz Ferdinand, but the actual circumstances which precipitated the war are a bit more complex.
In 1914, Belgium had declared itself to be neutral in the European conflict; however, their treaty of neutrality was violated by Germany when the Germans invaded. The German position was that Belgian had negated its claim to neutrality by allowing French forces to travel through their country to attack Germany. The German response was vicious and brutal against the nearly defenseless Belgium. Civilians, including women and children, were rounded up and slaughtered, establishing the tone for the war. The rationale given for this action was that German troops believed that the civilians were enemy snipers despite any evidence to support this belief. The brutality displayed by the German soldiers was so reprehensible that it spurred England and other nations to enter the conflict.
President Wilson and the American populace were reluctant to enter the war. Because Germany and the Central Powers were initially circumspect in their attacks, Wilson believed that maintaining the US's traditional neutral stance was the best policy. While the German's attack on Belgium did stir public sentiment against the Germans, It wasn't until the sinking of the luxury ship, Lusitania, by a german submarine that the general public began to clamor for war. Germany offered assurances to to President Wilson that it would restrict its submarine attacks to military vessels. Nevertheless, onver the next two years, Germany continued its course of marine aggression culminating in enacting a policy of unrestricted attacks in 1917, and the US felt compelled to enter the war.