Bosnia was ruled by Austria-Hungary. They wanted independence and a terrorist group assassinated Archduke Franz Ferdinand there. This marked the start of World War I. Austria-Hungary blamed Serbia and declared war on the small country. Germany, who was Austria-Hungary's ally, declared war on Serbia's allies, Russia and France. To invade France, Germany crossed into Belgium and invaded it. Great Britain who was an ally of Belgium declared war on Germany. Soon almost all of Europe was at war. The US soon declared war on Germany after Germany attacked the Lusitania, an American ship. Soon Germany's team known as the Central Power lost the US team which was known as the Allied Powers.
