How does allegiant end?

In "Allegiant," the final book of Veronica Roth's Divergent series, Tris and her friends discover the truth about their society and the world beyond the wall. They learn that their society was part of a larger experiment to heal a damaged world. The story culminates in a tragic climax where Tris sacrifices herself to save her loved ones and ensure a better future for the remaining factions. The novel concludes with Tobias reflecting on her sacrifice and the hope for a new beginning for their society.