Though it began in Age 761, the Attack of the Saiyans conflict's origins go back to the Genocide of the Saiyans in which Planet Vegeta was destroyed by the tyrant and Galactic Emperor of Universe 7, Frieza who feared the raise of a Super Saiyan in addition having been ordered to do so by God of Destruction Beerus due King Vegeta's stinginess and the Saiyans brutal evil nature. However several Saiyans survived the destruction as they were off world at the time. Vegeta, Raditz, and Nappa survived and became subordinate to Frieza whom lied to them about Planet Vegeta's destruction with a cover story about it being destroyed by a meteor to ensure their loyalty, though in the anime they heard rumors of Frieza's involvement though Vegeta knew even if it were true it would be foolish to oppose Frieza unless he could be sure of victory.
Meanwhile, Raditz's younger brother Kakarot was sent to Earth to conquer the planet shortly before Planet Vegeta's destruction (in Dragon Ball Minus Bardock had a bad premonition causing him to convince Gine they should send their youngest to Earth to ensure his safety under the cover of sending him on a mission to conquer the Earth). Kakarot was found by Son Gohan who adopted him and named the boy Son Goku. Goku however was violent like most Saiyans and cared little for Gohan's kindness. However one day he hit his head causing him to lose his memory and become a pure hearted boy who came to see the old man as his Grandpa Gohan. Gohan trained Goku like steel with him excelling at the Martial Arts thanks to his Saiyan instincts. However tragically Goku ended up accidentally killing Gohan when he transformed into a Great Ape, though Goku himself had no memory of it, assuming that Gohan had been killed by the Great Ape monster that Grandpa Gohan had warned him about (which was actually Goku himself as Gohan had survived a previous encounter). Goku came to believe his Grandpa's soul was in his Grandpa's Four-Star Dragon Ball. Eventually Goku met Bulma who was searching for the Dragon Balls and left Mount Paozu with her to find the Dragon Balls setting him on a path to becoming one of the Earth's greatest martial artists saving it from various threats such as the Pilaf Gang, Rabbit Mob, Red Ribbon Army, and King Piccolo's Demon Clan. Eventually, Goku won the 23rd World Martial Arts Tournament after defeating Piccolo the son and reincarnation of King Piccolo. Goku went on to marry the Ox-King's daughter Chi-Chi whom he had mistakenly promised to marry in his youth due to thinking it was food though kept his word after defeating an upset Chi-Chi who reminded him of his promise and chose to marry her after his friends explained what marriage was. Chi-Chi and Goku settled down to married life having a son they named Gohan after the grandfather who raised Goku.
Meanwhile his brother Raditz continued to serve alongside his fellow Saiyan comrades, Nappa and Vegeta. However one of the planets they were assigned to conquer had strong inhabitants which would be hard with just the three of them and their Saibamen, so remembering his younger brother had been sent to Earth, Raditz decided to go to Earth in order to recruit his little brother.
Main article: Raditz Saga
Five years after Goku won the World Martial Arts Tournament, depicted at the end of Dragon Ball, Raditz travels to Earth to recruit him. However he finds the planet's inhabitants are still alive following an encounter with an unfortunate Farmer and seeks to uncover why his brother Kakarot has not destroyed all lifeforms on the planet. When arriving on the 12th of October of Age 761, he finds Kakarot, who turns out to be Goku. After revealing Goku's origins, Raditz attacks Goku and kidnaps Gohan, Goku's young son, threatening to kill him if Goku refuses to join him and their Saiyan comrades. Goku and Piccolo proceed to team up to defeat Raditz, putting their differences aside just for this occasion. After a difficult struggle against the Saiyan brute in which Piccolo loses his arm, Piccolo decides to use the Special Beam Cannon in an attempt to kill Raditz. Goku attempts to stall Raditz to give Piccolo time to charge the attack, but proves no match for his older brother. However, he manages to grab onto Raditz's tail, immobilizing him temporarily. Raditz begs Goku to release him so that he may leave Earth, and Goku, being the pure-hearted man he is, falls for Raditz's trick. Raditz proceeds to beat Goku severely, but hearing his father's cries, Gohan becomes furious and unleashes his hidden powers, escaping from inside Raditz's space pod, where Raditz had locked him. Exploding with rage, Gohan flies towards Raditz and smashes into his chest, badly injuring him.
Seeing his opportunity, Goku grabs Raditz and puts him in a Full-Nelson hold long enough so that Piccolo can fire the Special Beam Cannon again. Both Goku and Raditz are killed by the beam, but before Raditz dies he gives the message about the Dragon Balls to his cohorts, Vegeta and Nappa who promptly decide to use said Dragon Balls to wish for immortality instead of reviving Raditz as Raditz had believed. Piccolo, in his frustration, finishes Raditz off.
Having witnessed Gohan's potential, Piccolo decides to take the boy under his wing and train him. Though he is initially hostile towards Gohan, since he is the son of his greatest enemy, he soon grows to love Gohan like his own son and they form a strong bond. Elsewhere, Kami sends Yajirobe to gather the Dragon Team together for special training at Kami's Lookout in order to prepare for the Saiyans' arrival.
Meanwhile, on a special request by Kami, Goku is allowed to travel down Snake Way in the Other World so that he may seek out the famed King Kai for training as well. The journey down the long road is not an easy one: Goku falls off and ends up in Hell and is forced to face two ogres competitively in order to escape, and has a run-in with Princess Snake, only barely managing to escape her fury when he rejects her. In the end, Goku finally reaches King Kai's planet and undergoes a harsh training regimen which increases his strength exponentially. During his training, King Kai explains Goku's Saiyan ancestry to him, but tells him a different version of the planet's destruction.
Battle on Arlia (anime only)
On their way to Earth, Nappa and Vegeta land on a planet inhabited by an insect-like race. The two Saiyan warriors decide to allow themselves to be captured by King Moai's soldiers and imprisoned. King Moai orders them to fight his soldiers in a gladiator-like arena, whom Vegeta and Nappa effortlessly kill. King Moai's pet giant known as Yetti is unleashed to kill Vegeta and Nappa, but the monster is also annihilated with ease. They then proceed to kill the King himself, much to the praise of the prisoners, one of which regards them as heroes, but as they take their leave, Vegeta callously destroys the planet.
Arrival on Earth
Roughly a year later on the 3rd of November, 762, the two Saiyans arrive on Earth, around the same time Goku completes his training and begins his return journey down Snake Way, this time much faster than before. Upon arrival, Nappa blows up the East City, much to the dismay of Vegeta, who remarks that he could have destroyed one of the Dragon Balls. They then use their scouters to locate the two strongest warriors on the planet: Piccolo and Gohan.
Battle with the Saibamen
After arriving on the battlefield, Paprika Wasteland, the Saiyans stand off against Piccolo, Krillin, and Gohan. In a strange turn of events, Nappa plants some seeds in the ground and pours a strange green liquid on them. Six small green creatures known as Saibamen appear and attack the three warriors. Yamcha, Tien Shinhan, and Chiaotzu soon arrive and each fighter takes a turn to combat the Saibamen. Tien Shinhan fights first and defeats a Saibaman, which is then finished off by Vegeta for its failure. Yamcha fights the next one and manages to knock it out, but the creature surprises Yamcha by grabbing hold on him from behind and self-destructing, killing him immediately. Enraged, Krillin kills the majority of the remaining Saibamen, with the last one being killed by Piccolo.
With the Saibamen gone, Nappa takes on the Z Fighters by himself. Nappa quickly dominates the battle, beating Tien severely and even punching his arm clean off. In an attempt to stop the Saiyan brute's onslaught, Chiaotzu latches onto Nappa and self-destructs, but Nappa survives. Nappa then turns to Piccolo and Krillin, who manage to hold their own despite receiving some hits. Tien, mad with rage, focuses all his energy into one spectacular Spirit Tri-Beam, but only manages to damage Nappa's armor. Because of the sheer amount of energy used from the attack and literally putting his life in the attack, Tien promptly dies. With only three fighters left, Nappa and Vegeta agree to wait three hours for Goku to arrive.
However, Goku fails to arrive in the allotted time. After Krillin nearly decapitates Nappa with a Destructo Disc, the enraged Saiyan paralyzes Krillin with a single energy blast. In an attempt to buy Piccolo time to escape to save the Dragon Balls, Gohan manages to strike Nappa down. Infuriated by the sneak attack, Nappa almost kills Gohan, but Piccolo blocks the attack with his entire body, sacrificing his life to save Goku's son. With tears in his eyes, Piccolo thanks Gohan for being his only friend and dies at the young warrior's side. Gohan unleashes all of his sheer rage in a Masenko attack, however, it fails to successfully damage Nappa. Before Nappa can kill the young warrior, Goku finally arrives. After healing Gohan and Krillin, Goku takes on Nappa and overwhelms him with his increased strength. After realizing Nappa cannot defeat Goku, Vegeta orders Nappa to stand down, but in his anger, Nappa takes the opportunity to attack Krillin and Gohan, only to be paralyzed by Goku's desperate Kaio-ken Finish. Because of his failure, Vegeta kills Nappa, and proceeds to take on Goku.
Goku vs. Vegeta
Goku and Vegeta engage one another in an epic struggle. Vegeta, however, quickly gains the upper hand, but Goku gains more power with the Kaio-ken attack and topples Vegeta with the 3x Kaioken attack. Vegeta attempts to destroy the Earth using the Galick Gun attack, which Goku counters with a x3 Kaioken Kamehameha and wins the ensuing struggle by increasing to Kaioken x4. After being injured, Vegeta creates an artificial moon, transforming himself into a Great Ape and turns the tables completely. Outmatched, Goku distracts Vegeta with a Solar Flare attack and begins charging up for a Spirit Bomb. Just before he can launch it, Vegeta spots Goku and fires a mouth beam, injuring Goku and blowing away most of the Spirit Bomb's energy. Vegeta tortures Goku and nearly kills him before Gohan and Krillin intervene. Gohan distracts Vegeta while Krillin prepares the Destructo Disc to slice Vegeta's tail off. This fails after Vegeta dodges it, but Yajirobe, who had been hiding the entire battle, cuts the tail with his sword, bringing Vegeta back to his normal form.
Vegeta, in his rage, takes on Gohan. Krillin uses the remaining energy of Goku's Spirit Bomb and throws it at Vegeta, scoring a direct hit. However, Vegeta survives and resumes his assault, only for Gohan to transform into his Great Ape form after his tail grows back and he looks up at the artificial moon. Vegeta manages to cut his tail off, but is unable to dodge as Gohan's Great Ape body lands directly on him, crushing him. Still alive thanks to his armor but unable to continue fighting, Vegeta summons his space pod in order to leave Earth. Krillin catches up to Vegeta and prepares to kill him with Yajirobe's sword, but Goku telepathically asks Krillin to show him mercy and let him leave, since he enjoyed fighting Vegeta and hopes to face him again one day, also hoping that this act will make Vegeta change his ways as it once did to Piccolo. With great reluctance, Krillin accepts, but Vegeta snidely vows to return and make them all pay for humiliating him.
With Goku in the hospital, Vegeta sure to return, and the Dragon Balls gone due to Kami's death, all hopes of reviving the fallen fighters seems lost. However, Krillin realizes that there might also be Dragon Balls on Namek, Piccolo's home planet. Using the spaceship that Kami originally came to Earth in, Gohan, Krillin and Bulma travel to Namek to use the Namekian Dragon Balls in order to bring their friends back to life. But little do they know that Vegeta has also traveled to Namek in order to use the Dragon Balls for immortality, and so has another powerful villain, the Galactic Emperor Frieza which resulted in the Battle on Planet Namek.