I recently came across a reference (but no story title, dammit) to an early-Thirties story by Williamson about a multinational team of scientists stranded on Mars when their respective countries go to war back on Earth. The story was apparently in published in Wonder magazine. I got three Williamson collections from the library and didn’t find anything like that in any of them.
By the way, I found a publisher that is publishing the complete works of Williamson in multiple volumes; this link has the table of contents for each volume, with the date and location of each publication listed - this should help your search The Collected Stories of Jack Williamson