Final answer:
The final straw for a full-scale war in Europe was the assassination of Archduke Franz Ferdinand of Austria-Hungary in 1914. This triggered a series of alliances and escalated into World War I, a conflict paved by nationalism, imperial rivalry, and historical grievances, with the assassination serving as the immediate catalyst.
Step-by-step explanation:
The Assassination that Sparked World War I
The final straw that caused a full-scale war in Europe was the assassination of Archduke Franz Ferdinand of Austria-Hungary on June 28, 1914. This event triggered a series of alliances and treaties among European powers to come into effect. The assassination, carried out by a young Serbian nationalist, Gavrilo Princip, led Austria-Hungary to declare war on Serbia. This declaration then compelled Russia to come to Serbia's defense due to a treaty obligation, which in turn caused Germany to declare war on Russia.
The series of war declarations continued, with Germany declaring war on France and invading Belgium, drawing Great Britain into the conflict. This cascade of events contributed to the start of what would become known as the Great War, or World War I. It was a conflict stoked by nationalism, imperial rivalry, military alliances, and arms buildups, with roots stretching back to unresolved tensions from previous historical grievances, such as the Franco-Prussian War and territorial disputes over regions like Alsace-Lorraine.
These underlying factors, combined with the assassination that acted as a catalyst, finally tipped Europe into a large-scale war. Known as the "War to End All Wars," World War I reshaped Europe politically and geographically, set the stage for World War II due to unresolved issues and the imposition of harsh terms on the defeated powers, and ushered in a new era of warfare with modern, devastating weapons.