Important in creating an atmosphere favorable for the united states' entry into world war i was

Some background:The event that brought USA into WWI is the Pearl Harbour Incident, where Japna launched an surprise attack to the US Naval Base in Pearl Harbour.

The favorable factor is that she join the war late with sufficient resources and the morale was high among soilders, while the other nations were starting to worn out, already suffering from casualties. Not to mention America also had advanced technology and great economy to support her operation in WWI. This gave America a huge advantage in the war.