The First World War broke out because of a system of two major European Alliances. These started a war due to Germany's ruthlessness, and caused a European war. Then the nations' colonies joined in, and eventually all of the world's major powers had joined in, causing the First World War. Before the main events of the war, two main alliances had been formed. Germany had defeated France in the Franco-Prussian war in 1871. 3 000 French soldiers were …showed first 75 words of 1270 total…

…showed last 75 words of 1270 total…Britain. The USA declared war with Germany and Austria-Hungary on April 6 and December 7 1917 respectively. Hence, the First World War was caused by a fight between two major Euopean alliances, each of which had colonies overseas also fighting, and then other nations joining in because of its huge scale. The responsibility should be shared, but not equally shared, as Germany's ruthlessness is what caused the original European war, which escalated to form the First World War.