Lots of people have already written about how Superman and Wonder Woman are from other worlds. Kal-El was a baby refugee before he became Clark Kent and Superman, for instance, and Wonder Woman grew up on the Amazon island of Themyscira and decided to become an American as an adult.
Therefore, it's not a huge stretch to think about these golden age superheroes as fitting into an existing tradition of immigrant literature. Immigrant stories often have a fairly didactic message of mutual benefit. In "America and I," Anzia Yezierska writes, "Then came a light—a great revelation! I saw America—a big idea—a deathless hope—a world still in the making. I saw that it was the glory of America that it was not yet finished. And I, the last comer, had her share to give, small or great, to the making of America, like those Pilgrims who came in the Mayflower." The immigrant's contribution to the U.S. is thus both idealistic and practical: it requires the immigrant to love the nation's potential and work to achieve it. The message is that both the immigrant and the U.S. will be enriched by immigrants' vital contribution to the nation.
Early Superman stories engage in this kind of propagandistic championing of immigrant contributions to the U.S. as Superman is wholly Americanized by growing up in the U.S. and then uses his impressive strength to defend "truth, justice and the American way." That is some mutual benefit, right there: he's getting a home from us, and we are getting his powerful action and devotion in return. Harry Brod has commented in "Superman is Jewish?" that marginalized Jewish comics creators like those who created Superman, Jerry Siegel and Joe Shuster, were "creat[ing] an alternate, idealized version of America. ... Their strategy of assimilation by idealism worked" (3). The "other" could become an idealized hero figure by using his or her power to fight for an idealized nation, and those many marginalized authors and artists who created the various golden age heroes would be folded into the fabric of America.
Of course the heroic figure does not assimilate. He or she does not become a representative member of the society so much as a larger-than life metaphorical representation of the ideals of that society. The alter ego of the hero, however, IS able to assimilate. While the alter ego of the hero is often read as a power fantasy, I would argue that in addition to the fantasy of a slight, seemingly powerless man being secretly incredibly physically strong and powerful, the Superman figure also embodies the twin fantasies of successful assimilation and integration that are so often at odds in immigrant literature. In fact, Kal-El gets to have his cake and eat it too, as he spends his days as the mild-mannered Clark Kent. No one would ever suspect Clark Kent of being more - or other - than he seems to be. Even his many trials and tribulations are those of a totally normal American weakling. In the person of Superman, however, Kal-El avoids assimilating in appearance. He adopts the ideals of his new nation (as he understands them) and uses his considerable strength and power to uphold them, wearing his own native garment and not pretending for an instant to be less than he is. He gets to be both.
In the (admittedly, much less) I've read of Wonder Woman, she presents a similar dichotomy of experiences: able to blend in entirely and successfully whenever she wants; able to employ the strengths of her upbringing and ancestry whenever she wants. That's nice for her, sure, but it is also noteworthy that there is a flip side to the benefits of the alter ego: creating a secret identity is not just an assimilation wish fulfillment. It also recasts the "otherness" of the immigrant as a powerful tool to be used for America's benefit. In both these cases the hero can hide his or her otherness when necessary and also activate the power associated with otherness at will. This ability casts that otherness as power.
The creators of golden age superheroes were essentially inventing their genre, cobbling together traditions out of component parts of other genre traditions like the Western, detective story and boy's adventure, as well as the propagandistic elements of immigrant literature. By now, the field has changed drastically. The superhero narrative has been codified into its own genre, one that like the western, is associated with American mythmaking. As Jerry Robinson has discussed, the superhero genre has a a variety of tropes, including that the superhero: is an adult with an alter ego; has a younger sidekick or protege; has a supervillain archenemy; and has an origin story that either recounts the hero's onset of powers or his or her arrival in our nation or world.
Two texts that do so are Ms. Marvel and The Shadow Hero, which I recently paired at the end of an American Lit II class unit about immigrant literature. They seemed like a fitting coda because both these heroes are first generation Americans, and as such, innovate the immigration stories of their parents and their superhero predecessors for a new era and population.
The Shadow Hero tells "the story of Hank Chu, a mild-mannered Chinese American teenager growing up in a fictional 1930’s Chinatown." His immigrant mother presses him to become a superhero, and it turns out that his immigrant father has brought with him from China a spirit that may enable this.
Ms. Marvel, so far, tells the story of "A Muslim-American teenager growing up in Jersey City, Kamala Khan [who] gained shape-shifting powers" and then took on the role of Ms. Marvel that Carol Danvers had used before. In Volume 1 especially, Kamala's immigrant parents put a variety of pressures on her that are at odds with the pressures of her society and her discovery of her new powers. Both she and Hank battle expectations as well as villains.
Both of these are origin stories. Instead of arriving in the U.S. with significant powers ready to use them for America's benefit as Kal-El and Diana both did, each of these heroes develops powers during adolescence, after growing up in the U.S. As coming-of-age stories, these narratives comment on the first-generation experience in America by merging many of the tropes of the superhero genre that emerged in the golden age of comics with the American monomyth version of the hero's journey.
Also, in their very American-ness, Kamala Khan and Hank Chu return readers to the type of message that I believe the golden age of superheroes began with: they support the idea that the U.S. benefits from new people arriving to love it.