What happened between the 1937 through the 1940?

Between 1937 and 1940, the world saw significant political and military tensions leading up to World War II. In 1937, Japan intensified its invasion of China, while in Europe, Adolf Hitler's Germany continued its aggressive expansion, annexing Austria in 1938 and occupying Czechoslovakia. The Munich Agreement of 1938, which allowed Germany to annex parts of Czechoslovakia, failed to prevent further aggression. By 1939, Germany invaded Poland, prompting Britain and France to declare war on Germany, officially starting World War II.