There are some things you need to fix. A lot of the images show the Google images layout. To fix this, you can just right click the flag and save the image to get it without the extra stuff. If it doesn't give you a big enough image, open the site and save it from there (Wikipedia always works when you click on the image to open the bigger view and save it from there). Fix the image of the Kingdom of Italy's flag. Second of all, there need to be better type-ins: Japan for "Japanese Empire" (really Empire of Japan), USSR (Union of Soviet Socialist Republics) for Soviet Union, Germany for "Nazi" (which should be listed as Germany), and USA, United States, and United States of America for "United States of America (48 Stars)". Another thing is that you should add the yellow box so that people don't just guess random countries and get them right. Also, just capitalize the country names. It makes it look better.
You should also add the countries of China (with ROC (Republic of China) as a type-in), New Zealand (with NZ as a type-in), Thailand, Burma (which was not fully occupied by Japan), Mongolia, and Finland (who was co-belligerent, not occupied, with the Germans during the Winter War, but switched sides after signing an armistice with the Soviet Union.