1. Dual Alliance and Triple Entente:
- The Dual Alliance was a defensive alliance between Germany and Austria-Hungary, formed in 1879.
- The Triple Entente was a loose alliance between Britain, France, and Russia that developed in response to the Dual Alliance.
2. Assassination of Archduke Franz Ferdinand:
- The assassination of Archduke Franz Ferdinand of Austria, heir to the Austro-Hungarian throne, in Sarajevo on June 28, 1914, triggered a series of events that led to the outbreak of World War I.
3. Ultimatum to Serbia:
- Austria-Hungary issued an ultimatum to Serbia, blaming it for the assassination and making demands that were considered unacceptable by Serbia.
- Russia, a Slavic ally of Serbia, began mobilizing its military in support of Serbia.
4. Germany's Declaration of War:
- Germany, as an ally of Austria-Hungary, declared war on Russia on August 1, 1914, and on France, Russia's ally, on August 3, 1914.
5. Activation of Alliance Mechanisms:
- The outbreak of war between Germany and Russia, and subsequently France, activated the alliance mechanisms that bound other countries to join the conflict.
- Britain, as an ally of France and Belgium (which had been invaded by Germany), declared war on Germany on August 4, 1914.
6. Domino Effect:
- As the war progressed, other countries became involved, either due to existing alliances or because of their own interests and concerns.
- Italy, a member of the Triple Alliance, initially remained neutral but later joined the Allies in 1915, seeking territorial gains.
- The Ottoman Empire sided with Germany and the Central Powers, while Japan, an ally of Britain, joined the Allies in 1914.
7. United States' Entry into the War:
- The United States initially maintained a policy of neutrality but was drawn into the war in 1917 after the sinking of the British passenger ship Lusitania by a German U-boat and Germany's unrestricted submarine warfare.
- The United States declared war on Germany on April 6, 1917, tipping the balance of power in favor of the Allies.
In summary, the system of European alliances created a chain reaction that led to the involvement of more and more countries in World War I. The assassination of Archduke Franz Ferdinand, the subsequent diplomatic crisis, and the activation of alliance mechanisms resulted in a domino effect that drew various nations into the conflict, eventually culminating in the United States' entry into the war.