Why didn't the US focus on Japan first in WW2? (Short Animated Documentary)

From History Matters

The United States entered World War 2 in the wake of the Japanese sneak attack on Pearl Harbor. However, upon joining the allies Roosevelt's government and the US military agreed to a 'Europe First' policy whereby Germany would be the primary focus and once defeated, the allies would turn their attention to Japan. But given how angry Americans were feeling over Pearl Harbor, why didn't the US aggressively focus on destroying Japan first. To find out watch this short and simple animated histor...