You're leaving out the entire purpose of the blockade: preventing Japan from importing oil and other goods to supply their massive invasion of China and Southea

You're leaving out the entire purpose of the blockade: preventing Japan from importing oil and other goods to supply their massive invasion of China and Southeast Asia. The attack on Pearl Harbor wasn't unprovoked, but failing to do anything would likely have ended up with the U.S. being attacked by a stronger set of allied opponents.