Jaydn was given the option to attend the Valentine Party, but chose to have class instead. What caused the attack on Pearl Harbor? The attacks caused The United States Navy to lose over 20 naval vessels, eight of those being battleships, over 200 airplanes, and over 2,400 navy men. The next day, December 8, 1941, President Roosevelt asked Congress to declare war on Japan. They agreed with his request on the same day. Three days later, Japanese allies, Germany and Italy, declared war on The United States. Shortly after, the United States responded by declaring war on European Forces. This was the United States' official entry into World War II.