Deleted User said 8 years, 4 months ago:

There are two main events that triggered the First World War to occur:

1. On July 28, 1914, Archduke Franz Ferdinand, heir to the throne of the Austro-Hungarian Empire, and his wife, Sophie, Duchess of Hohenberg, were assassinated by Slav nationalist Gavrilo Princip, who was 19 years old back then. Austria blamed Serbia for the assassinations.

2. German troops invaded Belgium, which the British government had previously promised to protect, and Luxembourg, leading Great Britain to declare war on Germany. When Germany attempted to invade France, British troops helped French troops in halting the Germans.