The Atlantic has just begun publishing a 20-part series of articles on "World War II in Photos". So far, two articles have been published. The first is "Before The War". Here are a couple of sample photographs from it, reduced in size to fit this blog.
during the Second Sino-Japanese War
in flight above Spain on May 30, 1939, during the Spanish Civil War
The second article is "The Invasion of Poland and the Winter War".
was hit by torpedoes from the German submarine U-29, and sank within 20 minutes
along a road in a snow covered forest on January 17, 1940
There are many more (and larger) photographs in each article. With 18 more instalments to come, this series looks like it'll be well worth following. You might want to bookmark the series page and keep an eye out for the weekly articles. I plan to read them all.