Why was the sinking of the Lusitania a turning point for Americans who

Why was the sinking of the Lusitania a turning point for Americans who had recently been in favor of neutrality?

Answer:

ANSWER
An ideal answer will include:
1. A discussion of Germany’s usage of submarines, or U-boats, and their effect on safe travel and safe trade.
2. The fact that the Lusitania, and the Falaba before it, was a passenger ship.
3. A discussion of the Zimmermann telegram that demonstrated Germany was looking for alliances to side against the United States.
4. Provide a concise and effective conclusion.