Which event brought Britain into World War I?

• A. The sinking of the Lusitania.
• B. The Zimmerman Telegram.
• C. The invasion of France through Alsace-Lorraine.
• D. Germany's invasion of Belgium.

Answer: (D)

The event being tested is Britain’s entry into World War I due to Germany’s invasion of Belgium in 1914. Britain had promised to defend Belgian neutrality under the 1839 Treaty of London, and when German troops violated that neutrality to sweep through Belgium on the way to France, Britain saw it as a direct challenge to the balance of power and to its own security. That violation triggered Britain to declare war on Germany, bringing it into the conflict.

The other options don’t fit as the immediate cause. The Lusitania sinking occurred in 1915 after Britain had already entered the war and mainly influenced opinion in the United States. The Zimmerman Telegram (1917) also affected U.S. involvement rather than Britain’s entry. The invasion of France through Alsace-Lorraine was the broader frontline consequence of German strategy, but Britain’s decision to go to war hinged on Belgium’s violated neutrality and the obligation Britain felt to uphold it.