Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
Suggest a reason why the US declared war on Germany in 1917.

### Response:
The United States declared war on Germany in 1917 due to the German government's policy of unrestricted submarine warfare, which was a threat to U.S. merchant vessels and declared neutrality. U.S. public opinion strongly favored the Allies, and President Woodrow Wilson and the Congress decided to join the war against Germany.