Dominion — Arthur J. Burks

Deep in the heart of South America's jungles, explorers Leyson and Horton found the source of the fantastic rumors which had been alarming government officials. And the facts they found were stranger than the wildest stories they had heard, for here were a race of metal men, the New People. And here, behind the scenes, was Von Glauber, sworn follower of the swastika, making a madman's dream come true. For the metal giants had been made to rise and conquer, and have dominion over the entire world!
First published in Science Fiction Stories, July 1943