President Alma Coin was a strict, no-nonsense leader who was willing to let people die so that her mission could be fulfilled, and eventually, Katniss figured this out. This was a big reason why Katniss eventually killed President Coin.
Katniss kills Glimmer, Marvel, and Cato in The Hunger Games. Glimmer's death occurs by chance. Katniss drops a tracker jacker nest on the Career Tributes' camp while they are sleeping, and Glimmer is stung to death before she can get away. Marvel is the first person that Katniss intentionally kills.
She expected their years of friendship would make it harder to kill. But she knows her one and only true ally is Peeta, so she decides she must kill Finnick now. Katniss climbs down from the tree, determined to kill him now before he has the chance to kill her.
Using knowledge from the movie and the books, let's break down how The Hunger Games ends. Coin killed Prim to destroy Katniss because, as Boggs (Mahershala Ali) explains before his death, Katniss is her biggest threat to maintaining her power over Panem because of the influence Katniss has over the people.
Hunger Games: Why Katniss Ends Up With Peeta, Not Gale
How did Gale kill Prim?
Before the Capitol battle, Gale had explained to Katniss his series of bombs designed to feed off human compassion: a small bomb would go off, and then when medical aid rushed in, a second bomb would go off, killing those people as well. Incidentally, it's this exact type of bomb that took Prim's life.
By killing Coin, Katniss ensured a chance for a peaceful and fair country, avenged her sister's death, and liberated Panem from the fascist government. The Hunger Games franchise is still an iconic series of books and movies, with the latter truly cementing the property as an international phenomenon.
In the end, Katniss and Gale grew apart, as many childhood friends and young loves do. She needed something different in her life, and with Gale's link to Primrose's death, Katniss found a reason to cut ties. If Katniss ever wanted to find comfort again, she knew she had to return to Peeta for the long term.
Mags (Lynn Cohen) was a willing participant in the 3rd Quarter Quell. Despite knowing she wouldn't make it out of the arena alive, viewers grew fond of Mags as she was not only willing to volunteer for Annie to be in the Hunger Games, but stepped into the poisonous fog to sacrifice herself with no hesitation.
Even in the Games, she was trying to save the one she loved, and now that both factors were taken from her life, it made sense that she would question her existence. Additionally, Katniss was in great pain and still suffered from the trauma of the war. Death to her also meant a relief.
Katniss feels betrayed, most of all by Haymitch, who used her and Peeta. Eventually she wakes to find Gale there. He's badly injured and tells her the Capitol bombed District 12 after the Games. He got Prim and Katniss's mother out in time, but the District 12 is gone.
Snow can't stand to see a young woman betray a young man's affection—his view of what happened 65 years ago. And so he takes out his old, festering wound on Katniss.
In The Hunger Games series, Katniss killing President Coin instead of President Snow surprised many. Still, it was because Coin was revealed to be a ruthless leader with her own political interests.
By killing President Coin, Katniss risked her safety in order to not only avenge Prim's death but also gift the people in Panem a chance to live in a peaceful and fair country for everyone. Katniss was incarcerated for a time, and she was sent back to District 12 after she was deemed unsuitable for a trial.
Both Morphlings die during the Hunger Games in Catching Fire, after the female tribute from District 6 protects Peeta from the monkey mutations that attack the tribute. She dies in Peeta's arms while looking at the sunset.
Chia Mags kisses Finnick on the mouth to briefly let him know that this is the last time she will see him. It's her way of saying "Goodbye" but in a more affectionate way.
President Snow sees her as an enemy since her combination of popularity and low-level defiance constitutes a threat to his power. He dreams up The Quarter Quell as a way of getting rid of her and murders Cinna in front of her as a way of rattling her just before she's tossed into the arena.
She later realizes, after a conversation with the imprisoned President Snow, that President Alma Coin sent Prim to her death (which was caused by a hovercraft by the rebels) both to sway the Capitol citizens to Coin's side by making them think Snow was bombing the children, and to swing Katniss to her side through the ...
Although she will never know for sure, Katniss does recognize that she cannot be with Gale. She will never be able to forgive him for his idea — the parachute bombs — that killed Prim.
It's only implied that they get it on via snuggling and other affectionate acts in close quarters — but if you have read the book, they really imply that they took their relationship to the next level.
Peeta decides, though, that he will go out on his own to act as a diversion in case Katniss and the others need it. Gale gives Peeta his nightlock pill in case Peeta's captured. They leave early in the morning, bundled up and styled by Tigris. Cressida and Pollux go first, leading the way to the City Circle.
Essentially, Katniss was afraid that if she was to kill President Snow, then the whole revolution fails, and the rivalry would still continue. Therefore, Katniss had to sacrifice by killing Coin in order to end war, and knew that Coin couldn't do anything better than Snow to save the Panem.
After reading the book and watching the film, it seems clear that Lucy Gray realizes Snow was responsible for the death of his friend Sejanus Plinth (Josh Andrés Rivera). If Snow could sell his best friend down the river for personal gain, it was only a matter of time until he did the same with her.
