Since Oz is a country entirely surrounded by a desert that turns any living flesh that touches it into dust and sends up poisonous fumes, its foreign policy is largely at its own discretion. Jack Snow’s The Magical Mimics in Oz indicates that Lurline found it already isolated, which is part of why she decided to enchant it. There do seem to be a few hints of Oz having more communication with its neighbors in the distant past, but as far as I can remember they’re all in post-canonical works. Fred Meyer and Adrienne Martinez’ short story “Mr. Thinman in Oz” attributes a magic carpet to Ozma’s great-grandfather Emperor Ozandahan, perhaps something he used to reach distant lands. The Emperor Ozroar (whom Joe Bongiorno identifies with Ozandahan) is said in Henry Blossom’s Blue Emperor to have gotten Kabumpo from a forest in Boboland. Everett Avila’s “The Tail of the Pink Goat” reports that the Blue Emperor ruled the territory now known as the Kingdom of Dreams, or at least I assume that’s why the land is ruled by a king named Archibald Dreams. And Jeremy Steadman’s Emerald Ring states that the island of Torr was an Ozian possession until its governor declared independence during a change of kings in Oz.
Ozma generally seems to have enough trouble maintaining her own kingdom, which has a lot of unexplored territories and dangerous areas. Nonetheless, pretty early on in her reign, she chooses to try to rescue the royal family of neighboring Ev from the Nome King. She takes a strangely aggressive attitude on this mission, despite having only twenty-seven people in her army, no direct access to magic (although Glinda is presumably keeping tabs on her), and little knowledge of the intricacies of the situation.
While Ozma has the moral high ground here (I don’t expect readers are supposed to agree with the Nome King’s argument that the King of Ev can do no wrong by definition), her way of dealing with the situation shows a lot of naivete. It’s fortunate she has a hen along, as Billina both produces the weapons that give the Ozites the upper hand and manages to overhear a key piece of information that lets her disenchant the King’s prisoners. Dorothy takes the Magic Belt that gives the King a significant part of his power and gives it to Ozma, leading to the Nome King repeatedly trying to retrieve his property.
Ozma forms an alliance with Ev, and Road indicates that she does the same with Ix, Noland, Merryland, Hiland/Loland, Foxville, and Dunkiton.
The Nome King remains an enemy, however, and it’s his invasion of Oz in Emerald City that leads Ozma and Glinda to pursue an isolationist policy with Oz protected by an invisible barrier in addition to the desert. It’s not clear how the barrier works or how long it lasts, but it apparently doesn’t stop the Nome King from getting back into the country and attempting conquest a few more times. In “Tik-Tok and the Nome King,” which presumably takes place after the barrier is created at the end of Emerald City, the King angrily breaks Tik-Tok when he comes to the Nome Kingdom and rudely demands some new parts. His steward Kaliko is able to put the mechanical man back together, and the King gives him jewels to try to smooth things over with Ozma. The Great Jinjin Tititi-Hoochoo removes Roquat/Ruggedo from power and replaces him with Kaliko, who is very careful not to anger Oz. He only takes King Kitticut and Queen Garee of Pingaree as prisoners when assured they have no connection with Oz, and Dorothy decides she’s going to to march into the Nome Kingdom with a basket of eggs and demand their release anyway. Again, these actions likely lead to alliances with Pingaree, Rinkitink, and Boboland; but they don’t much help matters with the Nomes. When King Skamperoo of Skampavia makes Ozma vanish in Wishing Horse, Kaliko provides some assistance to Dorothy in getting her back, but secretly hopes she won’t be successful. Much of this is covered in the first part of Kenneth Shepherd’s essay “Imperial Oz.” At the time it ran in The Baum Bugle, someone wrote a letter complaining that it was actually a thinly veiled criticism of then-President George H.W. Bush’s policy in the Middle East. I doubt this was actually intentional, but thinking we should able to do anything anywhere in the world with no consequences has been the general American foreign policy for some time now. We don’t have access to a Magic Belt, however.
Later books show Oz allying itself with other nations, including the Silver Island, Rash, and the Red Jinn‘s territory in Ev; but this is pretty much entirely because someone associated with Oz stumbles upon them. It’s in Pirates that Ozma seeks out a policy not just of intervention, but of flat-out imperialism. She gives Captain Salt permission to “take possession of new countries and set the flag of Oz on far islands and mountain tops.” If we want to redeem Ozma somewhat here, we can say she was referring only to lands that are either uninhabited (not that that’s at all common in the Nonestic world) or are willing to enter Oz’s protection. The captain, however, takes it as his duty to claim lands that aren’t even aware of what he’s doing. As Eddie Izzard might say, he had flags.
Prince Alberif of Peakenspire is willing to allow Ozian colonists on his island, but this is the exception. The inhabitants of Lavaland and Patrippany aren’t even able to communicate with Salt and his crew. He even tries to make Ozamaland an Ozian protectorate, but Royal Explorers suggests that this didn’t really take. Why would a ruler who has so much trouble keeping her own subjects in line want control of overseas territory? Captain Salt suggests it’s so princes who are unable to inherit Ozian kingdoms due to their parents’ functional immortality will have places to rule, but we’ve already established that his interpretations might not be totally in line with Ozma’s. It might, however, be a little more difficult to excuse Ozma when, in Ozoplaning, the Tin Woodman claims possession of Stratovania for Oz, hoping it will bring him as much fame as Captain Salt. I’m pretty sure you’re already a lot more famous than him in most of the world, Nick.
Since Salt spends most of his at sea, we don’t actually see how Ozma feels about his actions. Surely Nick would know whether Ozma wants him claiming countries, though, right? The way Ozoplaning frames it is that he just can’t understand why anyone WOULDN’T want to be subject to Ozma. To be fair, Jellia Jamb doesn’t think this is a good idea. Regardless, King Strutoovious of Stratovania then invades Oz, and Ozma basically disarms him by removing the power from his blowmen’s horns.
While she obviously doesn’t want him invading any other countries, what if someone else attacks Stratovania?
Pirates is also where Ozma magically restores a former king of Menankypoo who was unpopular enough that his subjects pushed him into the ocean. Indeed, the implication is that they disposed of him because he wanted to pursue a more aggressive foreign policy, while they just wanted to continue their lazy, isolated existence. While Clocker, who is said to have put these ideas into the king’s head in the first place, was apparently being reprogrammed in Oz, who’s to say the ruler won’t once again start proposing invasion? Oz presumably had no dealings at all with Skampavia or the chocolate star before their leaders decided to invade, so these are cases where Oz is purely on the defensive. They don’t do much of anything to Skamperoo, trusting that his magic horse can keep him in line; while Jenny Jump turns the chocolate soldiers into toy tin soldiers and the Wizard of Oz melts their general.
In Lucky Bucky, Ozma, Glinda, and the Wizard relocate a volcanic bakery in the Nonestic Ocean to Lake Quad near the Emerald City. The bakers don’t seem to have any problem with it, but couldn’t the Ozites have at least asked first?
Foreign policy is a tricky matter. You’re never going to be able to please everybody, and even actions that seem to be morally right can lead to trouble in the future. It’s interesting to note that even a fairy queen of a supposedly utopian land makes a lot of mistakes in this area. But it’s okay, because she has magic and narrative on her side.
Seriously, though, I’ve been reading deconstructions of some well-known fantasy series (for instance, here are takes on Narnia, Xanth, and Harry Potter), and it’s amazing how much problematic material you don’t notice on first readings. To my mind, it’s usually not enough to dismiss an entire series. At least Oz tends to keep the preaching to a minimum and give significant roles to female characters. The talking animals in Oz also seem to be less marginalized than those in Narnia. Still, there are quite a few issues that we can’t ignore. Admittedly, Ruth Plumly Thompson was probably worse than L. Frank Baum in this respect, but it’s not as if Baum is free from blame either.