Why the U.S. Entered WWII

CAUSE AND EFFECT INFOGRAPH

Rise of Totalitarian Regimes

CAUSE: The Rise of Totalitarian Regimes was one of the reasons the U.S. entered the war. The reason they entered because of this is because of totalitarian countries like Japan and Nazi Germany,
EFFECT: Since Germany and Japan were totalitarian countries with strong military forces, their people were unable to exert any opinion on their government.

German U-Boats in the Atlantic

CAUSE: The German U-Boats and the Battle of the Atlantic was the longest and arguable the most important battle of WW2. It started on the very first day of the war and didn't end until the very last day of the war.
EFFECT: The allies (United States, United Kingdom, and Canada) defeated Nazi Germany in this battle. This was key if they ever wanted to invade Europe.

Cash and Carry Policy

CAUSE: Cash and carry was a policy requested by US President FDR at a session of the United States Congress on September 21, 1939, right after the outbreak of war in Europe. It replaced the Neutrality Acts of 1936. The revision allowed the sale of material to countries we are at war with, as long as the recipients arranged for the transport using their own ships and paid immediately in cash.
EFFECT: This was mostly directed at Nazi Germany making them mad.

Lend-Lease Act of 1941

CAUSE: The Lend-lease Act of March 11, 1941 permitted the President of the United States to "sell, transfer title to, exchange, lease, lend, or otherwise dispose of, to any [country whose defense the President deems vital to the defense of the United States] any defense article". This pretty much further extended the Cash and Carry Policy.

EFFECT: This made Nazi Germany even more angry at the U.S.

Bombing of Pearl Harbor

CAUSE: The Japanese surprise bombed Pearl Harbor.
EFFECT: This made the U.S. start war with Japan.