World War I in Photos: Animals at War

World War I in Photos: Introduction A century ago, an assassin, a Serbian nationalist, killed the heir to the throne of Austria-Hungary as he visited Sarajevo. This act was the catalyst for a massive conflict that lasted four years. More than 65 million soldiers were mobilized by more than 30 nations, with battles taking place around the world. A century ago, an assassin, a Serbian nationalist, killed the heir to the throne of Austria-Hungary as he visited Sarajevo.