Answer: a declaration of war against Japan.
Step-by-step explanation:
Japan attacked the US base at Pearl Harbor on December 7, 1941. On December 8, the United States declared war on Japan. Italy and Germany both declared war on the United States on December 11, to defend Japan, as they had signed the Tripartite Pact of mutual defense of one another. That same day (Dec. 11), the United States then declared war against Germany and Italy.