I'm going to say Fire Emblem: Genealogy of the Holy War.

Beware, BIG spoilers if you've never played this game and have interest in it. If there are spoiler tags, I don't know how to use them and apologize.

Holy War is often regarded as the finest writing in the Fire Emblem series, and rightfully so. It's pretty much Game of Thrones Fire Emblem, right down to having a Jon Stark and and other similarities.

The game has considerable arguments against imperialism without really cramming it down your throat, and I'll try to explain in short.

In the first generation of the game, you play as Sigurd and there are 2 other important characters alongside him - Quan and Eldigan. All 3 hail from a noble house from their country and have considerable political influence. They are also best friends behind the scenes with Eldigan going out of his way to protect Sigurd early on in the story when he's off fighting his imperialistic wars in the name of Grannvale.

In the first chapter of the game after the prologue, Sigurd invades Verdanne. Before the level starts, he is visted by Eldigan whom asks him; why do I find you about to invade Verdanne and on the border of Agustria? Sigurd explains that a noble woman has been kidnapped by Verdanne and cause they won't give her up, he's going to invade them and conquer them. By the end of the chapter, that happens. Sigurd conquers the entire country under the name of Grannvale (unlike the other FE games, Holy War is notable for having HUGE maps that cover entire countries and usually long battles that involve dozens of units).

As a result of Grannvale's aggressive actions conquering another country, Agustria (Eldigan's country) suddenly feels threatened by Grannvale and they fear that at any moment, they too will declare war and invade them. The next chapter takes place there and Sigurd's actions have snowballed to the point that Agustria has a big civil war between their houses and Eldigan is thrown in prison and deemed a traitor cause he don't throw his support directly behind the prince who killed his father to take the throne. The next chapter, Sigurd wages war and conquers most of Agustria to get to the castle with Eldigan and free him. To his surprise, Eldigan is not happy to get out of the dungeon and realize that half of his country is now under Grannvale's control.

In Fire Emblem, there is a trope of characters named after Camus (as he was the first going back to the very first game). The Camus characters are usually the most well written characters in the games. You meet them when invading other countries and they usually are sympathetic to the protagonist and offer support, but they refuse to betray their country, making them an enemy, usually a boss at the end of a map. These are the characters you end up feeling bad about having to kill to progress through the game. Eldigan is the Camus of this game.

In Chapter 4, the story has advanced several months with Sigurd governing over Agustria and it explains that Grannvale sends their own governors to put in charge of the conquered castles, who now are under their control. The story further explains that the Grannvale governors quickly begin to exploit the citizens of the country and establish their rule to further enrich themselves. Another war breaks out in the other half of the country as the king decides, he's going to push one last ditch effort to try and retake the country. This is when Eldigan calls to arms and decides that he is willing to fight his bestfriend on the battlefield and die in the name of his country for a corrupt king, rather than see his country be turned into a puppet state for Grannvale.

Depending on how you play the chapter, if you put some time into leveling up Lachesis (Eldigan's sister), you can have her approach his unit and talk to him and then you don't have to face him as a boss (and he gives her an Earth Sword which is useful). But if you approach him as Sigurd, Eldigan's text is "I've heard enough Sigurd" and he'll attack you and probably kill you with his overpowered holy weapon.

A lot of fans in the FE communities often argue that Eldigan is the dumbest character in the game, but I strongly disagree. No, he's not stupid at all. Unlike Sigurd, Eldigan can actually see the true intents of Grannvale occupying his country and realizes that they are never going to give the country back. He knows something is up with how they conquered Verdane before they entered his country and Eldigan basically decides he'd rather die for his country under a corrupt king than be stuck in a puppet state to an empire.

As the game progresses though, Holy War shows more imperialistic overtones with how the Grannvale empire is created through Sigurd's wars of conquering countries and how Sigurd more or less, is just a useful fool to the real powers that be that are orchestrating this giant empire.