In Gulliver's Travels, what is the significance, if any, of the order in which Gulliver’s journeys take place?
You might want to approach this question by considering the way in which the sequence of adventures that Gulliver has relates to one of the key themes of the novel, which is the way that claims of moral superiority and righteousness are often thinly veiled masks that hide physical superiority as what allows one group of people to subjugate another. Consider how Gulliver himself experiences this as it is his great size and superior physical might that allows him to help Lilliput defeat their enemies. His second adventure likewise shows him the importance of might by placing him in a world where everyone else is bigger than him. In fact, he is enslaved by the first giant that finds him. Each journey presents the dominance of might masquerading as moral superiority and righteousness in different ways. Think of how the Laputans maintain their power over Balnibarbi because of their implicit belief that they are more rational, even though the reader might disagree. Likewise, the enslavement of the Yahoos by the Houyhnhnms is justified through their cultural and moral sophistication. The location of each journey in turn forces us to examine the way that "might vs. right" is presented and each location in turn develops Swift's presentation of the way in which any claim of moral superiority becomes very hard to justify. Consider how Gulliver himself presents colonialism after returning to his own lands at the end of the novel:
[T]hey go on Shore to rob and plunder; they see an harmless People, are entertained with Kindness, they give the Country a new Name, they take formal Possession of it for the King, they set up a rotten Plank or a Stone for a Memorial, they murder two or three Dozen of the Natives, bring away a Couple more by Force for a Sample, return home, and get their Pardon. Here commences a New Dominion acquired with a Title by Divine Right... the Earth reeking with the Blood of its Inhabitants.
Each location in turn develops a messy picture where "Divine Right" or moral justification is often used as merely a smokescreen to mask physical superiority. The order of Gulliver's journeys helps present this theme to us through its exploration of the theme in very different contexts.