The Saiyan Army was the military force of the Saiyans. They were led by King Vegeta and served under Frieza and the Planet Trade Organization. They serve as minor, but important antagonists in Dragon Ball Z.
Prior to being annexed by Frieza, the Saiyans fought the Tuffles in the Saiyan-Tuffle war. After a ten year long struggle, the Saiyans completely annihilated the Tuffles after a full moon arose, allowing them to transform into Great Apes and eliminate the Tuffles. The Saiyans then colonized the planet and renamed it Planet Vegeta after their leader, King Vegeta.
In Age 732, the Saiyans were peacefully annexed by Frieza and conscripted into the Galactic Frieza Army. The Saiyan Army fought in hundreds of conflicts for Frieza, and had a very high success record, earning Frieza's respect.
After Bardock's team of low-class Saiyans defeated the Kanassans, something even Frieza's elites were unable to do, Frieza began to worry that the Saiyans would rebel against him and defeat him and secretly plotted to kill them all. When King Vegeta learned of this, he staged an invasion of the spaceship, but was killed by Frieza. Bardock also tried to stop Frieza, but was obliterated along with Planet Vegeta, and most of the Saiyan race when Frieza launched a Supernova at them.
However, several Saiyans survived, including: Goku, Vegeta, Nappa, Raditz, Broly, Paragas and Turles. Vegeta, Nappa and Raditz continued invading planets for Frieza, not knowing that he had blown their planet up, while Goku was sent to Earth as a baby to conquer it.
Turles also at some point escaped the destruction of Planet Vegeta and founded a group of space pirates, seeking to find a planet suitable to plant the Tree of Might, which grows fruit that possess immense power.
Eventually, Goku and Vegeta became the last remaining Saiyans along with Vegeta's younger brother, Tarble, who was sent away from Planet Vegeta long before it got blown up.
Planet Trade Organization