What was the most important event propelling the United States into the Grand Alliance with Great Britain and the Soviet Union during WWII? A.
Germany's invasion of the Soviet Union
B.
the Japanese attack on Pearl Harbor
C.
the discovery of Nazi concentration camps
D.
the America First policy

i believe your answer is d)

the monroe doctrine is the best known u.s. policy toward the western hemisphere. buried in a routine annual message delivered to congress by president james monroe in december 1823, the doctrine warns european nations that the united states would not tolerate further colonization or puppet monarchs.

"germany's geographic location was an advantage when it was on the offensive in the war because it was situated next to an extremely wide river, the rhine, which was difficult for the allies to cross."

the answer would more than likely a.)falling crop prices  

hope the answer is right and ,either way have a nice day.