You started a war that you don't know how to end.... The missiles you launched burned a village to the ground.... You're invaders. Your ship landed in our territory.... You knew we were here when you sent an armed raiding party to capture one of us and torture him. These are all acts of war.
After another peace meeting between Clarke and Commander Lexa of the 12 Clans on the October 25, the Woods Clan and the Sky People were at a strained truce. The two allied factions joined forces against Mount Weather until Commander Lexa made a deal with President Cage Wallace of the Mountain Men and thereafter the Woods Clan and Sky People were no longer allied but under a strained truce.
When Chancellor Griffin decided to allow Farm Station survivors to move into Mount Weather, she broke this tentative agreement, causing the Ice Nation to strike back. With the help of Carl Emerson, the last surviving Mountain Man, the Azgeda blew up Mount Weather, causing the deaths of 49 Sky People. Because of this, the newly elected Chancellor Pike took a group of Sky People and massacred 300 sleeping Trikru warriors sent by Commander Lexa to protect Arkadia from any potential Azgeda attack.
In Pilot, the Delinquents arrive on Earth from the Ark, their dropship crash landing in the middle of the Woods Clan territory. Unaware they are not alone, the Delinquents sent a party toward Mount Weather. As they near their destination they are attacked. Jasper was speared presumably by Grounders; he was later found tied to a tree as live bait.
In His Sister's Keeper, Bellamy Blake suspects that his sister has been taken by the Grounders and forms a search party to find her. While out in the woods, the Delinquents come across Grounder territory. After the group splits, those still with Bellamy cross the territory and are unknowingly followed by Grounders. When the Grounders make themselves known, by killing Mbege, the Delinquents flee through the woods. In the process of fleeing, Diggs is impaled by a grounder trap. While searching for Diggs, Roma is speared in the chest, killing her. When the Grounders have the rest of the group surrounded, a Grounder blows a horn, to warn of acid fog which chases off the Grounders allowing the Delinquents to survive.
Later, when the group of Delinquents finds Octavia, they debate whether or not to kill the Grounder. The grounder stabs Finn in self-defense and Bellamy and the Grounder fight. The Grounder almost kills Bellamy,but Jasper knocks the Grounder unconscious. The group race back to camp to try and save Finn.
In Contents Under Pressure, Bellamy takes a small group out to find the Grounder who had taken Octavia. When the Grounder is brought back to camp, Bellamy, Miller, and Drew string him up in the top level of the drop ship. They proceed to try and get information from the Grounder.
When Clarke Griffin reveals that Finn is dying from the Grounder poison, Clarke gives Bellamy permission to torture the Grounder further. When the Grounder still refuses to give them the antidote, Raven Reyes resorts to electrocuting the Grounder. Octavia, who had been watching, grabs the blade and cuts her arm. Infected with the poison, she approaches the Grounder and asks him which vile is the antidote to the poison. The Grounder reluctantly gestures to the correct vile, allowing Octavia and Finn to take the antidote. Later, Clarke tries to clean the Grounder's wounds but Octavia takes over for her.
In Day Trip, while cleaning the Grounder's wounds, Octavia learns that he does speak English and that his name is Lincoln. When Octavia realizes that Jasper Jordan is high off of Jobi Nuts, she hands them out to Miller and the rest of the camp. Once the camp is hallucinating, she helps Lincoln escape. Later that night, Bellamy asks Octavia if she helped the Grounder escape, to which she replies she didn't.
In Unity Day, Finn follows Octavia sneaking out of camp where he finds her with Lincoln. Finn tries to negotiate peace with Lincoln. Lincoln explains that he does not have the power to negotiate peace between The 100 and The Woods Clan. After Finn explains that more soldiers will be coming down from the Ark, Lincoln agrees to try and set up a meeting between his leader, Anya, and their leader, Clarke.
Finn comes to Clarke explaining that he's set up a meeting with the Grounder and tries to get her to negotiate peace. Clarke agrees and tells Finn she'll meet him at the front gate soon. Instead of going to get her stuff, she informs Bellamy about the meeting. Clarke asks Bellamy to follow them and to bring guns as backup. While on the way to the meeting, Clarke leaves a trail for Bellamy, Raven, and Jasper to follow.
When they reach the bridge, Octavia approaches Finn and Clarke. Lincoln appears, as does a group of Grounders. Clarke meets with Anya and explains that she wants peace. Anya says that the 100 started a war they don't know how to end. When Clarke explains they didn't start anything, Anya tells her that the 100 burnt down a village. Clarke accuses Anya and the Grounders of spearing Jasper, to which Anya claims she knows nothing about. Clarke tries to put the past behind her and negotiate peace. Anya wants to know why she should negotiate peace with the 100 when more Sky People would be coming down, and asked if Clarke can guarantee that these people would hold to the peace agreements set by Clarke. Clarke tells her she will try.
Down below, Jasper, Bellamy, and Raven watch on. When Jasper spots Grounders in the trees with their bows at the ready, he panics and believes the Grounders are preparing to shoot Clarke, Octavia, and Finn. With the intent to protect his friends, he shouts for Clarke to run and begins to shoot at the trees. Clarke looks over to see Jasper shooting and Anya pulls out a knife to kill Clarke. Bellamy shoots Anya in the arm just in time, saving Clarke. Lincoln takes an arrow meant for Octavia and tells the Delinquents to run back to their camp. When the group of Delinquents return to camp, Octavia and Finn are furious. Finn at Clarke for not trusting him and Octavia at Jasper for ruining their only chance at peace.
In I Am Become Death, the 100 learn that Murphy was tortured by the Grounders for information about the Delinquents' camp. Clarke inspects his wounds and confirms he was tortured. Later, the 100 begin to get sick. Clarke orders all those sick into the drop ship. When Bellamy appears, Clarke explains that Murphy has been used by the Grounders as biological warfare in retaliation for what happened at the bridge.
When Clarke sends Octavia to go ask Lincoln for the cure, Octavia learns that there is no cure. His people use it to weaken before they attack, and they will be attacking the Delinquents at dawn. Octavia rushes back to camp to warn the others about the impending Grounder attack.
Later on, Bellamy, Jasper, Finn, and Raven try to come up with a way to stop the attack. Raven gets the idea to blow the bridge up. When Bellamy asks who plans to blow it up, Finn reluctantly accepts the job. When Finn goes to do it, however, he learns that Raven has already taken the bomb and is trying to do it herself. Raven sets up the bomb but before she can detonate it, she becomes violently sick with the virus Murphy brought to camp. Finn rescues her from the bridge as the Grounders approach. Jasper and Monty, after a few failed attempts, successfully shoot the bomb and blow up the bridge, delaying the Grounder attack on their camp.
In The Calm, Anya captures Finn and Clarke when they went out hunting for more food. Anya demands Clarke help a young tribeswoman named Tris who is Anya's second in command. Anya reveals that the girl had been injured in the bombing of the bridge. When the attempt to save the girl fails, Anya orders Finn to die and Clarke be kept alive. Anya plans to use Clarke as their healer because theirs died in the explosion. It is revealed to Clarke that the Grounders still plan on attacking the camp and that the camp would be gone by morning. Clarke kills a Grounder, Caliban, and tries to get back to camp to warn the others. She is caught in a Grounder trap, however, and knocked unconscious.
In We Are Grounders (Part 1), the Delinquents prepare for the war against the Grounders. Raven sets up landmines while Bellamy and his militia set up fox holes.
Meanwhile, Clarke meets Tristan, a man who has been sent to kill her people. Tristan orders another Grounder to kill Clarke. The Grounder advances on Clarke and Clarke is once again knocked unconscious. When Clarke awakes she finds herself on a horse. The Grounder is revealed to be Lincoln. He saved both her and Finn, by killing one of his own people.
Lincoln takes the two into the Reaper tunnels which are the fastest way to get back to the 100's camp. Lincoln claims he only saved Clarke and Finn for Octavia. He believes that what his people are doing to the 100 is wrong. Later, Lincoln leads the Reapers away from Clarke and Finn. Clarke and Finn make it back to camp and warn the others. Clarke announces they are leaving before the Grounder Scouts that Lincoln warned them about appear.
In We Are Grounders (Part 2), The 100 leave camp for the ocean. While on their journey, Drew is killed by a throwing weapon. The 100 retreat back into their camp. The decision to stay and fight is made. Clarke and Raven come up with a plan to make the rocket "blast off". Bellamy plans to give them as much time as they need. Before the battle, Finn leaves to go find a coagulant that will save Raven's life. At Lincoln's cave, he finds Lincoln alive and well. Lincoln gives him the coagulant to save Raven and follows Finn back to camp to help Octavia. Before they leave, Finn gets a "really bad idea".
As the Grounders continue to bait the 100 to use all their ammo, Monroe flees one of the foxholes when she runs out of ammo. Bellamy tries to call her back but, their fox hole is attacked by Grounders. A Grounder injures Miller and another attempts to choke Bellamy to death. While trying to choke Bellamy, the Grounder is killed by Octavia. However, Octavia is injured by an arrow to the thigh. Bellamy orders Miller to get back to camp as he helps Octavia.
Later, Finn and Lincoln appear with a group of Reapers chasing after them. When the Grounders see the Reapers, Finn and Lincoln disappear from sight. The Reapers are quick to join the fighting and kill Grounders. Once most, if not all, of the Reapers are killed, Tristan continues the attack on the 100 by breaking down the main gate. Inside the camp, the 100 are preparing to enter the drop ship. Clarke claims that Jasper needs more time to get the rockets ready to fire. She orders all gunners to stay at their posts while everyone else is to get inside.
Once the rockets are ready to fire, Clarke demands to wait until Bellamy and more of the others get inside. She goes outside to find Bellamy. When she does, she sees him fight Tristan and watches as Bellamy loses. Finn grabs a gun from one of the Delinquents and shoots Tristan just before he's about to kill Bellamy. Bellamy continues to fight Tristan. Finn gives Clarke a look and nods his head before he is grabbed by another Grounder. Clarke is led back into the drop ship by Miller and closes the door, leaving Finn, Bellamy and other Delinquents outside. Anya notices the door closing and quickly jumps in. Anya prepares to attack the Delinquents but is hit in the head by the end of Miller's gun. The 100 begin to beat and kick Anya. Just as Miller is about to stab Anya, Clarke stops him and announces that they are not Grounders.
Outside, Grounders being to climb on the outside of the drop ship. Inside, Jasper tries to fire the rockets but they fail. He quickly finds another source of energy and fires off the rockets killing every Grounder, Delinquent, and Reaper nearby.
In The 48, It is revealed that Tristan, Bellamy, Finn, Monroe, Sterling, and an unnamed Delinquent have survived the explosion. Bellamy finds Monroe and Sterling and asks them how they survived. Sterling mentions that they went to find the Ark in hopes to bring back reinforcements. They then hear movement and see Tristan on a horse with Finn and an unnamed Delinquent being dragged along behind him. The unnamed Delinquent falls and can't get back up. Tristan gets off his horse and grabs the Delinquent and slits his throat. Finn protests and Tristan mentions that he killed only one and he lost three hundred.
Back at camp, it is revealed that Raven, Murphy, and an unnamed Grounder have survived the explosion. The unnamed Grounder enters the drop ship and spots Raven lying on her side. He approaches and when he touches her, Raven rolls over and shoots him point-blank in the face.
Later, Bellamy tries to attack Tristan to get Finn back. However, Tristan once again defeats Bellamy. With Bellamy tied up, Monroe and Sterling watch on. Monroe tries to be brave and runs out to help Bellamy and Finn, with Sterling following. However, before the two can attack Tristan, he is shot by Marcus Kane.
Rivo is also captured by the Sky People and is brought back to Camp Jaha for interrogation by Marcus Kane and Major Byrne. Kane later decides to abdicate his Chancellorship and take Rivo back to his village in order to broker peace with the Grounders.
In Many Happy Returns, Anya abducts Clarke and tries to take her back to her own people. But Clarke gets the drop on her, taking Anya as prisoner. Later while Clarke is distracted, Anya gets up and starts to fight her. Clarke ultimately wins, however, she doesn't kill her but instead hits her in the face numerous times. As they approach Camp Jaha, Clarke sets her free in an attempt to end the conflict with the Grounders. This is quickly ended as Anya is shot down by a member of the Camp Jaha Guard, thus continuing the war between the Sky People and Grounders.
In Human Trials, Kane and Rivo arrive at Rivo's village. Kane orders the Camp Jaha Guard to return to Camp Jaha and disarms himself before Rivo knocks him out and takes him prisoner. When he is dumped into a holding cell, Kane is shocked to meet his fellow prisoner: Thelonious Jaha.
In Human Trials, Finn sets fire to the Woods Clan's camp, takes everyone in that area hostage, and later massacres them by gunning them down, believing that they have murdered his friends.
In Fog of War, Gustus forces Kane and Jaha to fight to the death in order to get justice for the massacre. Kane slits his own wrists and The Commander sees that Kane's intentions are honorable and allows his friend Jaha to go, with a message (Leave or die), back to his people.
In Long Into an Abyss, Clarke manages to work out a truce with the Grounders after showing them that she can turn Reapers back into normal people. However, The Commander states that she needs one thing in return, and Clarke agrees to give her anything. The Commander says she needs Finn because the truce starts with his death. Nyko also attempts to kill Finn because of the massacre he had committed.
In Spacewalker, The Grounders see Finn's death as a way to make amends. However, the Sky People refuse to give him up. Clarke tries to take Finn and help him escape. While running away a grounder ambushes Clarke, and Finn points a gun at the grounder, yelling at him to run away. Meanwhile, Indra threatens to march on the camp to Abby, as Indra says one of the grounders spotted Finn running through the woods in order to escape. Clarke, Bellamy, Murphy and Raven head to the dropship to hold their grounder and protect Finn. Ultimately, Finn gives himself up anyways. Just before his execution, Clarke comes in to say goodbye. She stabs Finn to prevent him from a more painful death. His death ultimately ends the conflict once and for all.
In Remember Me, Lexa gathers several Sky People to have a feast to make amends and discuss war terms against Mount Weather. When arriving at the village for the meeting many Grounders are unhappy to see Sky People free walk in their village, with a lot of Grounders yelling at them. Gustus is forced to beat one of them down in order to control the crowd. However, when an attempted assassination is thwarted when Gustus drinks poison, the Sky People are believed to have tried to kill Lexa. Raven Reyes is taken as prime suspect, and is taken to be executed. Lexa says that when she dies, the alliance dies with her. But, it is soon revealed that Gustus was the one who poisoned himself in order to break the alliance, because he believes the Sky People are a threat to Lexa. This results in Gustus's execution.
In Survival of the Fittest, one of Lexa's generals, Quint, argues with Clarke when they discuss how they will march on Mount Weather. When Clarke decides she needs to get air, Quint is seen attempting to kill Clarke by shooting at her with a bow and arrow. However, he is thwarted by Lexa, who stops him from killing Clarke.
In Blood Must Have Blood (Part 1), the relationship is strained when the Grounder Commander Lexa betrays the Sky People by saying they won't march on Mount Weather with them because of their newly formed truce with the Mountain Men. However, when the Mountain Men were wiped out, Lexa asked the Sky People to join the Coalition as the thirteenth clan in order to make peace with them. But when Chancellor Griffin decided to allow Farm Station survivors move into Mount Weather, this caused Azgeda to strike back. With the help of Carl Emerson, the last surviving Mountain Man, the Azgeda blew up Mount Weather, causing the deaths of 49 Sky People. Because of this, a newly elected Chancellor Pike took a group of Sky People and massacred 299 sleeping Trikru warriors sent by Commander Lexa to protect Arkadia from any potential Azgeda attack, causing the restrained relationship between the Sky People and the Grounders, once more.
Pike was later overthrown for his abusive power, and the Grounders, along with Kane, take Pike to Polis.
In Season Four, after Pike was killed and A.L.I.E. was destroyed, the Grounders still blame the Sky People, due to A.L.I.E.'s cruel actions, but King Roan of Azgeda has reinstated Sky People as the thirteen clan and declared, "An attack against Skaikru is an attack against us all." As things go back to normal, the conflicts between Skaikru and the Coalition has ended.
"You expect us to trust a Grounder? This is our home now. We built this from nothing with our bare hands! Our dead are buried behind that wall in this ground! Our ground! The Grounders think they can take that away. They think that because we came from the sky, we don't belong here. But they've yet to realize one very important fact: We are on the ground now, and that means we are Grounders!"
"I'm letting you go. I'm not weak, but I'm not like you. Our only chance against Mount Weather is if we fight together. To beat them, we'll need our technology and your knowledge of this world. I know my people will help. The question is, will yours?"
"So, now we're trusting Grounders to punish Grounders? I'm sorry Madam Chancellor, but I lost more than half of my remaining people yesterday. And four times the many since we landed. In my experience, Grounders understand one thing - strength. It's simple, we need to hit them now, we need to hit them hard."
"This morning on the muddy field, our people paid tribute to those who have been taken from us by sending a message to the Grounders. This land is ours now. Resist and you will be met by force. Fight and you will be greeted by death. Today is a new beginning. Mark it down remember it, just like the Grounders will remember it."