1. Why and when the US joined the war.
1.1. Japan was taking over islands in the Pacific trying to carve out their own empire. Japan took over some European colonies while they were fighting the Germans in Europe.
1.1.1. This expansion threatened the US interest in the Philippines.
1.1.1.1. The US placed an embargo, a ban on trade, on Japan for oil and scrap iron until Japan returned to their original borders. This would severely hurt their industrial society.
1.1.1.1.1. During peace discussions, the Japanese decided to launch a surprise attack on the naval base at Pearl Harbor. The US enters WWII.
2. Short Term causes
2.1. Hitler signed a surprising Non-Aggression Pact with Stalin in which they agreed they would not attack each other in the event of a war. Hitler also agreed to give half of Poland to Stalin once he invaded.
2.2. Hitler invades Poland in September of 1939.
2.3. Great Britain and France realize that Hitler will not stop and decided to declare war on Germany in September of 1939.
3. Long Term Causes
3.1. Treaty of Versailles
3.1.1. The Germans all but lost their military and their economy crumbled as a result of losing their oversea colonies and the the harsh reparations they were forced to pay.
3.1.2. The Germans were very resentful toward Europeans for the harsh conditions placed on them by the treaty.
3.1.3. As a result of the chaos created in Germany, a man by the man of Adolf Hitler will rise into power and use German resentment toward other Europeans to push his agenda and eventually lead the World into a Second World War.
3.2. Failure of the League of Nations
3.2.1. The League of Nations was created to prevent another war, however, it was very weak and ineffective.
3.2.2. The League had little power to stop acts of aggression such as when Mussolini invaded Ethiopia or when Japan invaded Manchuria. This gave Hitler confidence to start disobeying the treaty knowing the West was unwilling to take actions against aggressive behavior.
3.3. Failure of Appeasement
3.3.1. Appeasement is the granting of concessions to a potential enemy in order to maintain peace.
3.3.2. Hitler began to disobey the treaty
3.3.2.1. Hitler rebuilt the military which was forbidden in 1935
3.3.2.2. Hitler marched troops into the demilitarized zone in the Rhineland in 1936.
3.3.2.3. Hitler annexed Austria in 1938 (not allowed by the treaty).
3.3.2.4. Hitler demanded the Sudetenland of Czechoslovakia where many Germans lived.
3.3.2.4.1. This event created fear in the West. Neville Chamberlain visited Hitler and allowed him to take the Sudetenland region provided he would not take over any more territory. Hitler agreed....he lied.
3.3.2.5. Hitler invaded the rest of Czechoslovakia.