Which of these was a factor in the united states entrance in world war i?
a) the invasion of poland
b) japan's invasion of china
c) the axis threat to the panama canal
d) german unrestricted submarine warfare

D) German Unrestricted submarine warfare 

~Hello there! ^_^

Your question: Which of these was a factor in the United States entrance in World War I?

Your  German unrestricted submarine warfare was a factor in the United States entrance in World War I.

The answer is option D.

Hope this helps~

Contributing factors  leading  to the harlem renaissance were the great migration of african americans to northern cities, which concentratedambitious  people in places where they could encourage each  other, and the first world war, which had created new industrial work opportunities for tens of thousands of people.