The First World War, a conflict that reshaped the geopolitical landscape of the 20th century, officially began on July 28, 1914, when Austria-Hungary declared war on Serbia. This declaration was the culmination of a complex chain of events set in motion by the assassination of Archduke Franz Ferdinand just five weeks earlier, on June 28, 1914. While the assassination provided the immediate catalyst, the war was the result of deep-seated tensions and a rigid alliance system that had divided Europe into two hostile camps.
The Immediate Trigger: Sarajevo and the Ultimatum
The spark that ignited the powder keg of Europe occurred in Sarajevo, the capital of Bosnia. On June 28, 1914, Gavrilo Princip, a Bosnian Serb nationalist affiliated with the group Mlada Bosna, assassinated Archduke Franz Ferdinand and his wife Sophie. This act of violence was seen as an intolerable affront to the Austro-Hungarian Empire. In response, Emperor Franz Joseph I sought and received a "blank cheque" of support from Germany, promising unconditional backing for whatever action Austria-Hungary decided to take against Serbia.
The Alliance System: From Regional Crisis to Continental War
What transformed a regional dispute into a world war was the intricate web of alliances that bound the major European powers. When Austria-Hungary issued an ultimatum to Serbia on July 23, 1914, and declared war on July 28, the continent's alignment came into play. Russia, bound by Slavic kinship and treaty to Serbia, began mobilizing its forces. Germany, allied with Austria-Hungary, viewed Russian mobilization as an existential threat and declared war on Russia on August 1, 1914. This action triggered the next phase of the conflict's expansion.
Germany's Strategic Gamble
Germany's military doctrine, the Schlieffen Plan, required a two-front war against both France and Russia. To avoid fighting a war on two fronts simultaneously, the plan dictated a rapid invasion of Belgium to knock France out of the war before turning to face the slower-moving Russian army. When Germany issued an ultimatum to Belgium demanding free passage and was refused, Germany invaded on August 4, 1914. This violation of Belgian neutrality prompted Great Britain, bound by treaty to protect Belgium, to declare war on Germany. By August 6, 1914, the major powers of Europe were officially at war.
