Super-quick summary: Mexico was never completely "conquered," and people there are still fighting in various ways to keep their identities and histories.
Gibler has some remarkable thoughts to explain and summarize the idea of a conquered people vs. his "unconquered" title:
1) "Mexico is a nation divided, not conquered" (5)
2) quoting Bolivar Echeverria: "...the process of the Conquest in an enterprise that has not finished. ... the Conquest of America is still ongoing" (qtd. 5-6)
3) "I learned about the conquest of the indigenous civilizations in Mexico in elementary school. In class we learned the Spanish alphabet, we memorized the names of the colors, and we learned that the Aztecs were gone. ... It gave me nightmares--to think, a people no more, entire worlds gone: the Aztec, the Maya. That is what I was taught, the story of conquest, terrifying for its violence, but even more so for its finality. Worlds gone. Worlds no more. I did not yet know that the story of conquest is its own continuation, that the teaching of lost worlds is part of the sorcery that tries to make these worlds disappear" (11; emphasis mine). I mean... wow. The fact that *teaching* that a civilization was conquered and the people disappeared is part of making that civilization disappear by telling others that they don't exist anymore... wow.
4) "The amazing diversity of indigenous peoples [Gibler lists many different groups] across the territory now known as Mexico at the time of the Spanish incursion is typically reduced to the Aztec and Mayan empires, with brief mention of the disappeared Olmec or architecturally sophisticated societies like the Zapotec. This reduction is part of the conquest itself, of talking about the indigenous subjects of the past, not existing societies--the Mayan Empire collapsed...and the Aztec Empire fell to Hernan Cortes. They are gone. But over twelve million indigenous people remain, many denied both their history and their present" (22; emphasis mine) Again, by teaching over and over that these other peoples don't exist anymore, we're perpetuating the myth that they don't exist anymore. And of course by saying that a group doesn't exist, we delegitimize them, which means that we become blind to their current needs, too. If they don't exist, they don't need healthcare or shelter or income. They weren't conquered, but they're being forgotten and/or ignored by the system.
Gibler later points to "both historical and present human actions that forced (and continue to force) people into miserable situations" (97) and says that "poverty is not a state of nature, not an accident of history, poverty is both callous neglect by a complicit society and an ideological instrument used to decontextualize and naturalize forced destitution and new forms of political domination and social control" (103). As he goes on in the rest of his book, Mexico wasn't conquered, but it's been divided between those of poverty and those who aren't, those who had farmlands that have been taken over and those who did the taking over, those who've been exploited by the government and those who did the exploiting via corrupt business and dishonest politics, and explains those "lesser" people's "insistence on pursuing justice, their will to defend their dignity despite the blunt violence of the state" (185).
Towards the end of the book, he explicitly makes the point that revolting against conquest can be through violent actions (throwing rocks at police or the military [as retaliation for them shooting at you!], shooting guns, Molotov cocktails), nonviolent (peaceful protests, a peaceful alternate government that listens to everyone, taking over a radio station to broadcast your message), or even feeding protestors or naming your child in your native, indigenous language. Revolt against conquest, imperialism, and being disappeared can come in many forms, but the constant is the fight to make yourself heard.