The world went to war in the late 1930s, and early to mid 1940s. The comic book world reflected that. Artist Alex Schomburg was a comic book artist utilized on comic covers for his ability to use the assembled featured characters in a scene on the cover, regardless of whether they'd be together inside the pages. All Winners comics provided the prototype eventually for the comic book team of the Invaders, in issue 19 and 21. However, Roy Thomas and Sal Buscema, and later Frank Robbins created a team composed of the characters featured, usually, by Alex Schomburg.
The Invaders fought in WW II in Roy Thomas's Marvel Universe, and later, he committed the same love and attention in the DC Comics universe. The Justice Society and All Star Squadron played a similar role as the Invaders. Without the covers stirring the imagination of Roy Thomas, who knows how vital a role the Invaders would play in the eventual Marvel Universe?