If you count the years Japan was invading other countries like China and Korea it was probably 10 years or more, that's part of the war that's not taught about to much in history books or talked about period as their is alot of tension between the countries that Japan evaded. I think the reason is because of how cruel Japan was against the Chinese, See the book the "Rape of Nanking". Any way I don't think there will be much talking and teaching about that part of WWII until the old folks/leaders/politicians from those two countries are dead and gone, and then people will start talking about the atrocities Japan did too China and Korea and a bunch of other countries, more so then just footnotes in history books that Japan took over these countries.