The Causes of the war
The main causes that fueled the tension that started the war were Nationalism- pride in one's nation, Imperialism- establishing colonies, Militarism- building up arms, and Alliances- protection (secret allies).
The spark of the war
The assassination of the archduke of Austria-Hungary, Franz Ferdinand, and his wife. The couple had gone to a city in Serbia, and were killed by a Serbian terrorist group called the Black Hand. When Austria-Hungary heard the news, they believed that Serbia was behind the plot and demanded for an apology. Serbia refused to apologize because they had not been behind the plot. Austria-Hungary declared war on Serbia. Serbia's allies, Russia, France, and Great Britain, came to Serbia's aid. Germany came to help Austria-Hungary. 20 countries were involved in world war one.