Your Grace, Czechoslovakia yielded part of its land to Germany in 1938, but the latter did not take the whole country over until 1939. And, though the other countries you list did not enter the war until later, that doesn't alter the fact that the war was, in fact, going on. So, the answer to the question as set really remains '1939 - 1945'.
Technically the war in 1939 and 1940 was only a European and North African War, while the Sino/Japanese conflict was a separate Far East War. It was only the mega mistakes by the egotistical Japanese firstly in invading British held Hong Kong, Malaya and subsequently Singapore and secondly in December 1941 in Bombing Pearl Harbour that brought the USA into the war that made it truly a World War.
england stole one quarter of the worlds land and wealth to puff up it's ego . and postie has the dammed gaul to speak of egotistical Japanese.
Also Japan returned fire when they bombed Pearl Harbour, the yanks had been fighting against Japan for a couple of years prior to that.