The spark that lit the fuse of war was the assassination of Franz Ferdinand, the Archduke of Austria, in Sarajevo on June 28, 1914. The assassin was a Serbian nationalist who wanted Austria-Hungary out of the Balkans. Austria-Hungary sent the Serbian government an ultimatum that promised war if specific demands were not met. However, Russia had promised to protect the Serbs and threatened retaliation. Once Austria invaded Serbia on July 28, 1914, the German army began mobilizing for war, prompting the Russian army to do likewise. Assuming that the Austro-Hungarians would take care of the Russians, Germany declared war on France on August 3, launching an invasion through Belgium, which was a neutral country. Due to its alliance with Belgium, Great Britain joined the war against the Germans on August 7. Because of the complex alliances necessitated by the balance of power theory of European relations, the outbreak of war in a small corner of the continent flared up into a continent-wide conflagration.Learn more about World War 1
The Alliance system was one of the causes of World War I. Prior to the war there were two alliances. One was the Triple Alliance. This included Austria-Hungary, Germany, and Italy. The other alliance was the Triple Entente. This included Soviet Union (Russia), Great Britain, and France. The danger of these alliances is that if a member from one alliance declared war on a member from the other alliance, the conflict would quickly escalate. That is what happened in World War I.
When the next king of Austria-Hungary, Franz Ferdinand, was assassinated by a group of Serbian nationals, Austria-Hungary made a series of demands on the government of Serbia. When the government couldn’t meet all of these demands, Austria-Hungary, with the support and approval of Germany, declared war on Serbia. Since Serbia and Russia were very close friends and allies, Russia declared war on Austria-Hungary. Germany then declared war on Russia. France and Germany then declared war on each other. Eventually, Britain declared war on Germany when Germany invaded the neutral country of Belgium. Thus, what was originally a conflict between Austria-Hungary and Serbia quickly escalated into World War I, involving many countries throughout the world.