Question

the united states formally entered world war ii following the japanese attack on
nanjing
indochina
pearl harbor
the philippines

Explanation:

The Japanese attack on Pearl Harbor on December 7, 1941, prompted the United States to formally declare war on Japan the following day, entering World War II. The other options are incorrect: the Nanjing Massacre was a Japanese atrocity in China, attacks on Indochina and the Philippines occurred after the US entered the war.

Answer:

Pearl Harbor