Question

Which factor helped shift American opinion away from neutrality during World War I?

Answer 1

It was the targeting of merchant ships by German U-boats.  America realized that any ship including theirs was a target.  This was realized when the Germans sank the Luisitania.  Apart from that, the interception of the Zimmerman telegram where Germany pledged to support Mexico get back its territories from the U.S. led to American involvement in World War I.