The Kree are responsible for the creation of the Inhumans by experimenting on early man. The Supreme Intelligence forced the Kree into a new form of evolution the Ruul. The Ruul were the main instigators of maximum security.
The Kree started out as a primitive species sharing their planet Hala with the Cotati, a race of plantlike humanoids. Their planet was visited by the Skrulls, whom at the time where a peaceful race. They told the Kree and the Cotati that one of their species would be chosen to represent their planet in an interplanetary counsel. To chose which species it would be; they sent both the Kree and the Cotati to our moon, and told them each to build a city there. The species that built the best one would be chosen to represent the planet. The Kree labored over building a city (what is now the blue area of the moon) while the Cotati slept. When the Skrulls came back to the moon to award a winner they found that the Cotati had grown a huge garden while they slept! The Cotati won the contest. Furious, the Kree killed all of the Cotati and all of the Skrulls that visited their planet. They then used the Skrull ship to go to the Skrull home world and start the Kree-Skrull wars.
The Second Kree-Skull War was started by the Skrulls although the Kree were considering it. The Skrulls were led by Kylor, one of five claiming to be Emperor of the Skrulls. After capturing a Kree spy on one of their worlds they decided to strike first. When the Supreme Intelligence lost his mind, Nenora took over as Supreme Leader. Nenora was secretly a Skrull, but choose to remain a Kree and rule over all. She betrayed Kylor and her people. The Skrull campaign was taken over by Empress S'byll after Kylor's death. Nenora was defeated by S'byll when she gave Nenora her shape-shifting powers back. S'byll announced to the Kree their leader was truly a Skrull and that she had won the war. But, S'byll declared a peace. Tus-Katt was the highest ranking member available and he did not accept a peace, this was against all the Kree stand for. The best he could accept was a truce, which she accepted.
With the loss of the Supreme Intelligence and Nenora the Kree were left without a leader. Through manipulation, the Contemplator was able to get the pirate Clumsy Foulup to become emperor. The emperor was assassinated by Ael-Dan and Dar-Benn. They ruled the empire together, one being of blue skin and one of pink. When Thanos killed half the universe with the Infinity Gauntlet, the Kree automatically blamed the Skrulls for this unknown attack and prepared for war.
Ael-Dan and Dar Benn are killed by Deathbird during the Kree/Shi'ar War. After the Shi'ar are victorious due to the detonation of a Nega-Bomb over their throne world, Lilandra names Deathbird as regent. The whole Kree/Shi'ar War was orchestrated by the Supreme Intelligence as a way to jump start the Kree's evolutionary dead end, thus the Ruul was born. The Supreme Intelligence would later utilize this during the events of Maximum Security.
Major Story Arcs
The universe is over-run by the Annihilation Wave under the command of Annihilus. During this time Ronan the Accuser is declared a traitor and removed from his position as Accuser. He makes several new allies as he searches for the evidence to clear his name during the attack. He learns that the House of Fiyero, who are merchants currently in control of the Kree Empire, are responsible. Under their poor leadership, the Kree are easy targets for the Annihilation Wave.
The Fiyero Kree attempt to make a deal and join forces with Annihilus so that the war would end and they could go back to their commerce. Finding the proof of his betrayal, Ronan executes the enemies of the empire and is named leader of the Kree after the mercy killing of the Supreme Intelligence (who had already been lobotomized by the Fiyero). He is forced to cede several Kree Worlds (including Kree-Lar) and the Skrull Empire to Ravenous.
Still recovering from the Annihilation Wave , Kree space was infiltrated by the Phalanx using Galadorian Space Knights to take command over Kree military computers and weapons. It is only through the efforts of the soon to be Guardians of the Galaxy, Nova and Warlock that the Kree Empire is freed.
The Kree have several operatives on Earth, one of which (posing as a human named William Wagner) learns of the invasion prior to it occurring. He is attacked by two Skrulls just before the invasion, his fate is currently unknown.
Due to the Skrulls having abducted Black Bolt, the Inhumans form an alliance with the Kree in an effort to locate him. Ronan's price for this alliance is the hand of Crystal of the Inhuman Royal Family, a price her sister readily accepts. In the aftermath of the invasion the Inhumans leave the moon and travel to Kree space. They breach the barrier and confront Ronan who relinquishes the throne to Black Bolt.
War of Kings
During the Inhumans vengeance upon the Skrulls, a group of Shi'ar Warbirds are destroyed. Emperor Vulcan takes this as a challenge and sets his sights on conquering the Kree. The second Kree/Shi'ar War begins with the Shi'ar crashing the wedding of Ronan the Accuser and Crystal.
Black Bolt unleashes his weapon known as the T-Bomb, a device made with the Terrigen Mists, in the belief it will make everyone into Inhumans and end the war. With the detonation of the bomb, Black Bolt and Vulcan both perish, and it also creates a rip in space known as the Fault. With Black Bolt presumed dead, leadership of the Kree Empire is left to Medusa.
War of the Four Cities
It would come to be known that the experiment that created the Inhumans was prophesied to be the end of the Supreme Intelligence. Of the 100 races created, the Supreme Intelligence ordered them all destroyed. But five races survived. They would all come together to try and make the Earth their new home. The Inhumans, now lead by Black Bolt who had returned from the dead, left the empire in the hands of Ronan.
After all houses agreed to have him as leader, he and Crystal left for Earth to take complete control of the Kree Empire once and for all.
A group of Kree comes to Attilan to beg for sanctuary. They are attacked at first until they tell what they're there. They are then given tents to stay in, in the empty place of old Kree machinery. A group of Kree goes to kill the Inhuman Royal Family but is stopped. Another is gone to the Genetics Council to see if the hearing goes in their favor for them to stay permanently. Another group is mad that they have to beg the Inhumans, creatures they created for their slaves. They decide to go and destroy the one thing that gives them their powers, the Terrigen Crystals. When they get there, they are attacked by Inhumans. They tell the Inhumans they don't want to destroy the mists but use them. They tell them when the Avengers hit the Nega Bands above their city it did something to their genes so they could use the mists. Three went in and two came out alive.
The Kree attacked the Inhumans. They caught them very easily but with causalities. They separated the Inhumans by age, separating the old from the young. They sends machines over the city, for when Black Bolt screamed they picked the city up. The Kree wanted Ronan to help build up their status in the universe, they wanted to rule the Shi'ar. Ronan was to send the Inhumans to attack the Shi'ar.
Priests of Pama
The Priests of Pama are a group of pacifist Kree. They reside on Earth and have a relationship with the Cotati. They trained Mantis and Moondragon to be the Celestial Madonna.
The Supreme Intelligence evolved the remaining "true" Kree into Ruul using the forever crystal. The Ruul however have been removed from existence due to Genis-Vell.