World War I
World War One was thought to be the war to end all wars, but then ended up leading directly to another World War, thus being World War Two. World War One occurred from 1914-1918. The war all started with the assassination of the Austria-Hungary prince by Gavrillo Princip who was in the black hand group. The war then escalated when countries secret alliances with other countries forced them to stand up and fight or defend with their partnership in either the Triple Alliance or the Triple Entente.
The video above explains World War One including every country that was involved, giving reasons and examples of how and why the war happened.
The video above explains America's role through World War One.