Flash Gordon: The Fall of Ming (Sundays 1941-1944) is the third volume in the collected Flash Gordon comic strips by Alex Raymond and Don Moore, and the final volume containing Raymond's art. Raymond enlisted in the U.S. Marine Corps in 1944, and Austin Briggs, who was the artist of the Flash Gordon daily comic strips from 1940-1944, became the new artist of the Sunday comic strips immediately following Raymond's final strip, which was printed 7 May 1944. Later, upon his return from the war, Raymond devoted himself to another comic strip of his own creation, Rip Kirby.
SPOILER ALERT
The early 1940s mark a period of great change for this comic strip. We witness the fall of Emperor Ming and the establishment of a union of democratic republics on Mongo. Zarkov makes contact with Earth for the first time, and upon learning that the nations of Earth have been plunged into another great war, he, Flash, and Dale embark on a voyage home to do their part. We learn that Flash, too, is an inventor, and he lends his talents to the creation of new weapons based on the technology of Mongo to aid the war effort and, indeed, to thwart an invasion of the east coast of the United States. Aware that they need a greater supply of radium that miracle element so popular in early 20th century science fiction for these new weapons, and that Mongo has it in far greater abundance, Flash and company head back to Mongo... and promptly crash land in a previously unexplored region of that planet, where they become embroiled in toppling another despot.
I admit to missing some of our old friends from Mongo: Thun, Barin, Aura, Vultan, and others, but in the last strip in this volume we see Flash and Dale (where is Zarkov?) heading to Mongo. I assume that "Mongo" in this case refers to the nation of Mongo, since they are already on the planet Mongo, but one can never tell. I would also like to assume that they haven't forgotten their reason for returning to Mongo, since it hasn't been mentioned since they left Earth, but again, one can never tell. Maybe they will bump into Zarkov and he can remind them.
END SPOILER ALERT
At first, I thought I might conclude my reading of Flash Gordon with Raymond's departure from the strip, but cliffhangers being what they are, I might have to read on. Meanwhile, from the first decade of the Sunday strips alone, I have compiled lists comprising 20 different peoples, 47 different creatures, and 121 different technological curiosities of the planet Mongo, all of which can be found in the Lists of Mongo.