Which of the following was a major factor in the decision of the united states’ to enter world war i?
a. britain’s naval blockade of germany
b. germany’s unrestricted submarine warfare
c. vladimir lenin’s rise to power in russia
d. france’s fall to the central powers

The correct answer is:
b. Germany’s unrestricted submarine warfare

Specifically, Germany attacked some submarines that had US citizens on-board, and this was in violation of treaties that assured a safe submarine transport in the Atlantic ocean.

An additional reason was that Germany wanted to incite Mexico to start a war against the US.

The republican party