Final answer:
European countries quickly mobilized after the assassination of Archduke Ferdinand, triggering the outbreak of World War I due to complex alliances and treaties.
Step-by-step explanation:
Mary European countries quickly mobilized after the assassination of Archduke Ferdinand in 1914 because it triggered a cascade of alliances and treaties that bound countries to come to each other's aid in the event of war. This led to the outbreak of World War I.
One of the significant alliances during that time was the Triple Entente, which consisted of France, Russia, and the United Kingdom. When Archduke Ferdinand was assassinated, Austria-Hungary, an ally of Germany, declared war on Serbia, which was backed by Russia.
This chain reaction ultimately drew in other European countries as they honored their alliances and mobilized their forces for war.
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