Question

Why did the United States break diplomatic relations with Germany in 1917?

Germany refused to accept President WilsonÍs Fourteen Points.
Germany signed the Treaty of Brest-Litovsk with Russian Bolsheviks.
Germany declared unrestricted submarine warfare against all ships.
Germany sank the British liners Lusitania and Arabic in quick succession.
Germany offered to help Mexico recover Texas, New Mexico, and Arizona

Answer 1

The correct answer is Germany declared unrestricted submarine warfare against all ships.

What this means is that Germany claimed control of the seas and oceans and if anyone opposed it they would attack it with their submarines. The US joined the war 2 months later.