Prior to entering World War 1, what was the most important reason that the United States protested Germany's use of submarine warfare

I'm a little rusty on my history of this one but, if I remember correctly, being that America was a melting pot at the time, with still a strong sense of identity, the Germans sank a well-known tourist cruise ship, known as the Lusitania. Onboard were over one hundred American citizens. This strongly upset the United States, and Woodrow Wilson tried to avoid getting involved for the longest time, further upsetting his fellow Americans.

answer; i believe the correct answer is ( quakers);

basic principles: federalism, separation of powers, checks and balances, judicial review, representative democracy, limited government, rule of law, individual rights and responsibilities, consent of the governed, majority rule, popular sovereignty, equal protection.