In 1911 the British physicist Ernest Rutherford came up with the Rutherford model of the atom, which saw the atom as having a tiny, positively charged nucleus surrounded by orbiting electrons. The analogy to planets orbiting a sun was obvious; so obvious that as early as 1919 the writer Ray Cummings wrote a story, "The Girl in the Golden Atom", in which a scientist discovers that the electrons are planets, with their own submicroscopic inhabitants.
Although the view of atoms as miniature solar systems had been discarded by physicists by the mid-1920s, writers of fantastic fiction continued to tell tales of people from our own world shrinking themselves down to subatomic size and interacting with the inhabitants of electron-sized planets. The Shrunken Hero became one of the common tropes of early science fiction. In his anthology Before the Golden Age, Isaac Asimov included three stories of subatomic adventure: Capt. S.P. Meek's "Submicroscopic" and its sequel "Alwo of Ulm", and Henry Hasse's "He Who Shrank".
So it was only natural that as Harl Vincent continued writing science fiction during the Gernsback Era, he would eventually make use of the Shrunken Hero motif. As he often did, though, Vincent gave the tale an unusual twist. The people of his electron-sized planets are under the rule of the Prags, a race of rapacious telepaths. When our two heroes travel to the submicroscopic realm, they find themselves swept up in a revolution as the human-like inhabitants of Els make their desperate bid for freedom from their telepathic overlords.
The "master race" ideology of the 19th century was reaching its high-water mark in the 1920s, with the triumph of the Fascists in Italy giving rise to racial-nationalist movements throughout Europe. And of course, as an American, Vincent didn't need to look overseas to see the "master race" ideology in bloom when the Ku Klux Klan was at the peak of its power in the United States and the Jim Crow laws were at their worst. It is just such an ideology that motivates the Prags in their oppression of the other races of their atomic solar system, and the defeat of the Prags is also a defeat for their racist ideology.
Vincent's picture of the big-headed, telepathic Prags manipulating other races was echoed thirty-five years later in "The Cage", Gene Roddenberry's original Star Trek pilot, with its big-headed, telepathic Talosians manipulating Captain Pike and his crew. Given the obscurity of "Microcosmic Buccaneers" it is extremely unlikely that anyone in the Star Trek production team was aware of it; pushy telepathic aliens have always been a dime a dozen in science fiction, so there were plenty of other models for the Talosians. Nevertheless, it is gratifying to think that Harl Vincent was there first.