No society can exist forever in the shadow of another. As the settling of this world continues, and as the local culture develops and flourishes and begins to distinguish itself from what came before, the people will begin to yearn for the freedom to determine their own fate. This is the true, inevitable conclusion of any hominization: the permanent establishment of a free, independent government for the newly matured society.
The Victory scale is the in-game method to win. The scale starts as 'Colony' at 0% on the left and goes up to 'Independence' at 100% on the right (the wording is different on Earth, Lethe and TRAPPIST-1 planets but functionally it is the same). The percentage of victory can only be increased by spending Culture Points. Each point adds 5%. In addition to spending to 20 Culture Points on Independence, the five factions all have a unique additional criteria to achieve victory.
Culture Points are mainly earned from total population milestones (see table here), and randomly by certain events. Comparatively, to earn most Culture Points from population milestones is a faster, but more challenging path; as long as you have a bit of population, you can choose to sit back and wait for the Culture Points to trickle in through events, which takes longer but allows you to reach 20 points eventually with minimal effort. Realistically, your games would probably be a mix of both.
It appears if you have unspent culture points when your population falls beneath the relevant milestones, those culture points would be removed and you have to reach the milestones again to gain them, but if you have already spent them, you won't get them again.
As independence gets higher, random events may occur that hamper progress such as terrorism, sabotage from outside agents (destroys buildings) or offer a monetary bribe to the player to voluntarily lower the Independence percentage. This can happen at as low as 10% independence.
A good way to prevent such sabotage is to simply save up 20 culture points, and then spend them all on Victory all at once. Terrorists will not target worlds that are at 0% or 100% victory. This strategy can not work when playing in Expert Mode, because you can only spend 1 culture point towards victory once every 2 hours.
Victory texts differ for some worlds, such as those in the TRAPPIST-1 and Historical Earths campaigns, but for most worlds, they follow a standard script. This script differs based on the world's current habitability and culture, as well as the faction you chose.
It's been a long road, but you have transformed the people of [World] from a handful of explorers into a thriving civilization. Some [number] people now call [World] home, and more are arriving every day. With new forms of art and music and science and philosophy all unique to [World], this former colony has finally taken its place as a primary world in our growing interplanetary society, and a major player in the ever-evolving story of human history. You have shed the control of off-world powers, and the people of [World] are free to determine their own fate as a new, self-declared people.
Barren: Human life is still not possible on the surface of [World], and the discussion of this planet's future will likely continue for generations. Without the ability to support plantlife, [World] has a long way to go before your citizens will be able to breathe freely in the open air. Perhaps they never will: many of your people now support the idea of rejecting terraforming altogether. They say that [World] has its own beauty, separate from that of Earth, more alien and thus more precious.
Plantlife: Human life is still not possible on the surface, and the discussion of this planet's future will likely continue for generations. The introduction of plantlife has been proceeding smoothly, and the biosphere continues to evolve and thrive. Who knows, perhaps one day humans will walk unaided along the beaches and through the forests of [World]. For now, strolling through the alien grasslands in your pressure suit, you can't help but marvel at how far [World] has already come.
Habitable/Paradise: What was once a desolate world, hostile to any life, has become a garden for humanity to call home. Children play in the open air, taking for granted the alien landscapes all around them. This is their home, as real and natural as any on Earth.
Under your leadership the [faction] has become the foremost authority on interplanetary hominization. New societies are springing up on world after world, each modeled on your [plutocratic / democratic] system of government and [industrial / ecological] economy, focused on [economic / scientific] growth. You’ve effectively settled the terraforming debate as well, [encouraging/ discouraging] terraforming efforts on other planets by your own example.
A new chapter in the story of humanity is unfolding on [World]. Will you stay to continue it, or move on to new worlds out among the stars?