Aside from the mistake of allowing the German annexation of Austria, when the French and British tried to take affirmative action to stop Hitler's quest for power and land they made another significant mistake. Grossly underestimating and misinterpreting their soon-to-be enemy, Hitler was given a large part of Czechoslovakia at the Munich Conference in September 1938, in an attempt to keep peace. Instead of appeasing him and ceasing his thirst for conquest, this gift only increased his desire for more power and land.
Less than half a year later, Hitler had taken the rest of Czechoslovakia. At this point, the French and British still did not do anything to stop him, as they did not wish a repeat of the death tolls and trench warfare of WWI. To prevent encountering armies from the Soviet Union as he moved east, Hitler signed the Nazi-Soviet Non-Aggression Pact in August 1939, just over a week before attacking Poland, the soon-to-be first battle of World War II. The events of the timeline for WWII officially began on September 1, 1939, at 4:45 am, when Hitler staged what appeared to be a Polish attack on a German radio station. He manipulated the situation to make it appear as if Poland had attacked first, but in reality he took a prisoner, dressed them in a Polish military outfit, and shot them in the head. From the beginning, Hitler proved himself to be manipulative, calculating, and bloodthirsty, as this attack demonstrated.
While all of this was happening in Europe, conflict was simultaneously brewing between Japan and China. The Second Sino-Japanese War officially began on July 7, 1937, after decades of "incidents" between the two Asian counties. Japan wanted to dominate China so that they could control a number of resources; the rising notions of Chinese nationalism and self-determination aided in the fierce resistance against these invasions. These battles were not considered a part of the timeline for World War II until the Japanese attack on Pearl Harbour in 1941, which brought Japan and the United States - and their resulting allies - to war with one another.