The main alliances were the Triple Entente, consisting of Britain, France, and Russia, and the Triple Alliance, consisting of Germany, Austria-Hungary, and Italy. The Balkan Wars of 1912-13 had increased tensions between these alliances and brought them to the brink of war.
The spark that ignited World War I was the assassination of Archduke Franz Ferdinand, the heir to the throne of Austria-Hungary, on June 28, 1914, by a Serbian nationalist. This event triggered a series of diplomatic crises that led to the outbreak of war.
Here is the order in which countries declared war:
- July 28, 1914: Austria-Hungary declared war on Serbia, after Serbia had rejected its ultimatum to punish the assassins of Archduke Franz Ferdinand.
- July 29, 1914: Russia mobilized its army in support of Serbia. This prompted Germany to declare war on Russia the next day.
- August 1, 1914: Germany declared war on France, because France was allied with Russia.
- August 2, 1914: Germany invaded Luxembourg and Belgium, which was neutral territory. Britain responded by declaring war on Germany.
- August 4, 1914: Germany invaded France through Belgium. France and Britain were now at war with Germany.
- August 6, 1914: Austria-Hungary declared war on Russia. This completed the formation of the two opposing alliances, the Triple Entente and the Triple Alliance.
The system of alliances in Europe was a major factor in the outbreak of World War I. It created a situation in which a relatively minor conflict between two countries could quickly escalate into a full-scale war involving multiple countries.